+27 -17

dev/witness_dev.gleam

Reviewed

··· 2 2 import witness 3 3 4 4 pub fn main() -> Nil { 5 5 + configure_logging() 5 6 7 7 + // log a message 8 8 + witness.this(witness.Warning, "Some log message", [ 9 9 + witness.string("example", "you can add structured data"), 10 10 + witness.bool("also_bools", True), 11 11 + witness.float("and_floats", 1.23), 6 12 7 13 8 14 9 15 10 16 11 11 - 12 12 - 13 13 - 14 14 - 15 15 - 16 16 - 17 17 /// 18 18 fn configure_logging() { 19 19 // create a new config 20 20 - witness.empty_config() 21 21 - // log formatted text to stdout 22 22 - |> witness.with_sink(witness.Text, fn(level, message) { 23 23 - io.println(witness.level_to_badge(level) <> ": " <> message) 20 20 + witness.new("witness-dev") 21 21 + |> witness.with_global_fields([ 22 22 + witness.string( 23 23 + "my-global-field", 24 24 + "something i really need logged everywhere", 25 25 + ), 26 26 + ]) 27 27 + |> witness.with_console(witness.Debug, witness.Text) 28 28 + |> witness.add_file( 29 29 + witness.Warning, 30 30 + witness.Json, 31 31 + witness.new_file("testing.log"), 32 32 + ) 33 33 + |> witness.add_custom(witness.Debug, witness.Json, fn(message) { 34 34 + // Whatever you do in here has to be executed by the calling process 35 35 + // i.e. whoever ran `witness.this`, so try to keep processing low. 36 36 + // 37 37 + // On erlang you could, for example, `process.send` the log event 38 38 + // to a handler process somewhere in your supervision tree. 39 39 + io.println("Hello from my custom handler!\n" <> message) 24 40 }) 25 25 - // log as json 26 26 - |> witness.with_sink(witness.Json, fn(_, message) { 27 27 - // ideally you'd log this to a file using, for example, the erlang logger 28 28 - io.println(message) 29 29 - }) 30 30 - // apply this config globally 31 31 - |> witness.set_config() 41 41 + |> witness.configure 32 42 }

+14 -3

manifest.toml

Reviewed

··· 1 1 - # This file was generated by Gleam 2 2 - # You typically do not need to edit this file 1 1 + # Do not manually edit this file, it is managed by Gleam. 2 2 + # 3 3 + # This file locks the dependency versions used, to make your build 4 4 + # deterministic and to prevent unexpected versions from being included 5 5 + # in your application. 6 6 + # 7 7 + # You should check this file into your source control repository. 3 8 4 9 packages = [ 5 5 - { name = "gleam_erlang", version = "1.3.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleam_erlang", source = "hex", outer_checksum = "1124AD3AA21143E5AF0FC5CF3D9529F6DB8CA03E43A55711B60B6B7B3874375C" }, 10 10 + { name = "gleam_stdlib", version = "1.0.2", build_tools = ["gleam"], requirements = [], otp_app = "gleam_stdlib", source = "hex", outer_checksum = "0C5506589DF4C63DF5D6FFBB834562D6865C6C2AEE0019D7B37886BD6D128141" }, 11 11 + { name = "gleeunit", version = "1.10.0", build_tools = ["gleam"], requirements = ["gleam_stdlib"], otp_app = "gleeunit", source = "hex", outer_checksum = "254B697FE72EEAD7BF82E941723918E421317813AC49923EE76A18C788C61E72" }, 12 12 + ] 13 13 + 14 14 + [requirements] 15 15 + gleam_stdlib = { version = ">= 1.0.0 and < 2.0.0" } 16 16 + gleeunit = { version = ">= 1.0.0 and < 2.0.0" }

+278 -7

src/witness_ffi.erl

Reviewed

··· 14 14 % See the Licence for the specific language governing permissions and limitations. 15 15 16 16 -module(witness_ffi). 17 17 - -export([get_config/1, set_config/1, set_process_fields/1, get_process_fields/1]). 17 17 + -export([get_config/1, set_process_fields/1, get_process_fields/1, do_log/4, 18 18 + format/2, configure/1 , log/2, short_timestamp/0, rfc_3339_timestamp/0]). 18 19 20 20 + %% ------------------------------------------------------------------------------ 21 21 + %% Gleam ffi 22 22 + %% ------------------------------------------------------------------------------ 23 23 + 19 24 get_config(Default) -> 20 20 - case persistent_term:get(witness_config, undefined) of 25 25 + case ets:whereis(witness_config) of 21 26 undefined -> Default; 22 22 - Config -> Config 27 27 + _ -> case ets:lookup(witness_config, config) of 28 28 + [{config, Config}] -> Config; 29 29 + _ -> Default 30 30 + end 23 31 end. 24 32 25 25 - set_config(Config) -> 26 26 - persistent_term:put(witness_config, Config), 27 27 - nil. 28 28 - 29 33 set_process_fields(Fields) -> put(witness_process_fields, Fields). 30 34 31 35 get_process_fields(Default) -> 32 36 33 37 undefined -> Default; 34 38 Fields -> Fields 39 39 + end. 40 40 + 41 41 + % Log to the erlang logger 42 42 + do_log(Level, Message, Namespace, Fields) -> 43 43 + logger:log(Level, Message, #{domain => [witness, binary_to_atom(Namespace)], fields => Fields}). 44 44 + 45 45 + %% ------------------------------------------------------------------------------ 46 46 + %% Erlang logger configuration 47 47 + %% ------------------------------------------------------------------------------ 48 48 + 49 49 + configure({config, _Namespace, Sinks, _GlobalFields} = Config) -> 50 50 + case ets:whereis(witness_config) of 51 51 + undefined -> ets:new(witness_config, [named_table]); 52 52 + _ -> witness_config 53 53 + end, 54 54 + 55 55 + ets:insert(witness_config, {config, Config}), 56 56 + 57 57 + logger:update_primary_config(#{ 58 58 + level => all, 59 59 + filter_default => log, 60 60 + filters => filters(), 61 61 + metadata => #{} 62 62 + }), 63 63 + % remove existing handlers 64 64 + lists:foreach(fun logger:remove_handler/1, logger:get_handler_ids()), 65 65 + 66 66 + % add our handlers 67 67 + add_sinks(Sinks, 0). 68 68 + 69 69 + -spec add_sinks([witness:sink()], integer()) -> nil. 70 70 + add_sinks(Sinks, CustomIndex) -> 71 71 + case Sinks of 72 72 + [] -> nil; 73 73 + [Sink = {console, _, _} | Rest] -> add_sink(Sink, 0), add_sinks(Rest, CustomIndex); 74 74 + [Sink = {file, _, _, _} | Rest] -> add_sink(Sink, 0), add_sinks(Rest, CustomIndex); 75 75 + [Sink = {custom, _, _, _} | Rest] -> add_sink(Sink, CustomIndex), add_sinks(Rest, CustomIndex + 1) 76 76 + end. 77 77 + 78 78 + -spec add_sink(Sink, Index) -> ok | {error, term()} when 79 79 + Sink :: witness:sink(), 80 80 + Index :: integer(). 81 81 + 82 82 + add_sink({console, Level, Format}, _) -> 83 83 + Id = witness_console, 84 84 + logger:add_handler(Id, 85 85 + logger_std_h, 86 86 + #{level => Level, 87 87 + filters => filters(), 88 88 + formatter => 89 89 + {witness_ffi, 90 90 + #{format => Format, 91 91 + level => Level 92 92 + }} 93 93 + }); 94 94 + 95 95 + add_sink({file, Level, Format, 96 96 + {file_config, Path, MaxBytes, MaxFiles, Compress}}, _) -> 97 97 + Id = list_to_atom("witness_file_" 98 98 + ++ integer_to_list(erlang:phash2(Path))), 99 99 + logger:add_handler(Id, 100 100 + logger_std_h, 101 101 + #{level => Level, 102 102 + filters => filters(), 103 103 + formatter => {witness_ffi, #{format => Format, level => Level}}, 104 104 + config => #{file => binary_to_list(Path), 105 105 + max_no_bytes => MaxBytes, 106 106 + max_no_files => MaxFiles, 107 107 + compress_on_rotate => Compress} 108 108 + }); 109 109 + 110 110 + 111 111 + add_sink({custom, Level, Format, Handler}, Index) -> 112 112 + Id = list_to_atom("witness_custom_" 113 113 + ++ integer_to_list(Index)), 114 114 + logger:add_handler(Id, 115 115 + witness_ffi, 116 116 + #{level => Level, 117 117 + filters => filters(), 118 118 + formatter => 119 119 + {witness_ffi, 120 120 + #{format => Format, 121 121 + level => Level 122 122 + }}, 123 123 + config => #{handler => Handler} 124 124 + }). 125 125 + 126 126 + filters() -> 127 127 + [{domain, {fun logger_filters:domain/2, {stop, sub, [otp, sasl]}}}, 128 128 + {domain, {fun logger_filters:domain/2, {stop, sub, [supervisor_report]}}}, 129 129 + {progress_filter, {fun logger_filters:progress/2, stop}}]. 130 130 + 131 131 + %% ------------------------------------------------------------------------------ 132 132 + %% logger_formatter implementation 133 133 + %% ------------------------------------------------------------------------------ 134 134 + 135 135 + -type formatter_config() :: #{format => witness:format(), 136 136 + level => witness:level()}. 137 137 + 138 138 + -spec format(LogEvent, Config) -> unicode:chardata() when 139 139 + LogEvent :: logger:log_event(), 140 140 + Config :: formatter_config(). 141 141 + 142 142 + % logger_formatter api 143 143 + format(LogEvent, Config) -> 144 144 + try do_format(LogEvent, Config) of 145 145 + Formatted -> Formatted 146 146 + catch 147 147 + Error:Reason -> format_catch(Error, Reason, LogEvent, Config) 148 148 + end. 149 149 + 150 150 + format_catch(Error, Reason, LogEvent, _Config) -> 151 151 + Level = maps:get(level, LogEvent, error), 152 152 + [~"[WITNESS FORMATTER ERROR: ", 153 153 + atom_to_binary(Error), 154 154 + ~" ", 155 155 + io_lib:bformat("~p", [Reason]), 156 156 + ~"]\n", 157 157 + short_timestamp(meta(LogEvent)), 158 158 + ~" ", 159 159 + atom_to_binary(Level), 160 160 + ~": ", 161 161 + case maps:get(msg, LogEvent, undefined) of 162 162 + undefined -> ~"Unexpected message"; 163 163 + {string, Msg} -> io_lib:bformat("~p", [Msg]); 164 164 + {report, _Report} -> ~"Report data (formatter crashed)"; 165 165 + Other -> io_lib:bformat("~p", [Other]) 166 166 + end, 167 167 + $\n, 168 168 + io_lib:bformat("~p", [meta(LogEvent)]) 169 169 + ]. 170 170 + 171 171 + %% ------------------------------------------------------------------------------ 172 172 + %% text / json format 173 173 + %% ------------------------------------------------------------------------------ 174 174 + 175 175 + -spec do_format(LogEvent, Config) -> unicode:chardata() when 176 176 + LogEvent :: logger:log_event(), 177 177 + Config :: formatter_config(). 178 178 + 179 179 + do_format(#{level := Level, msg := Event, meta := Meta}, 180 180 + #{format := Format, level := SinkLevel}) -> 181 181 + {Message, ReportFields} = case Event of 182 182 + {string, Msg} when is_binary(Msg) -> {Msg, []}; 183 183 + {report, Report} -> report_to_fields(Report); 184 184 + {Format, Data} -> {io_lib:bformat(Format, Data), []}; 185 185 + Other -> {io_lib:bformat("~p", [Other]), []} 186 186 + end, 187 187 + 188 188 + MetaFields = fields(Meta, SinkLevel == debug), 189 189 + Fields = MetaFields ++ ReportFields, 190 190 + 191 191 + witness:format(Format, Level, Message, Fields); 192 192 + 193 193 + %% ------------------------------------------------------------------------------ 194 194 + %% unmatched fallback 195 195 + %% ------------------------------------------------------------------------------ 196 196 + 197 197 + do_format(#{level := Level, msg := Msg, meta := Meta}, _Config) -> 198 198 + fallback_format(#{ format_failed => unmatched, level => Level, msg => Msg, meta => Meta}). 199 199 + 200 200 + % fallback formatter in case the main one crashes 201 201 + fallback_format(Event) -> gleam@string:inspect(Event). 202 202 + 203 203 + 204 204 + %% Get fields associated with a LogEvent's metadata 205 205 + fields(Meta = #{fields := Fields, pid := Pid}, true) when is_pid(Pid) -> 206 206 + PidField = witness:string(~"pid*", io_lib:bformat("~p", [Pid])), 207 207 + % Check if this process is registered under any name 208 208 + PidFields = case process_info(Pid, registered_name) of 209 209 + [] -> [PidField]; 210 210 + {registered_name, []} -> [PidField]; 211 211 + % Add the name to the fields if it is 212 212 + {registered_name, Name} -> [PidField, witness:string(~"registered_name*", atom_to_binary(Name))] 213 213 + end, 214 214 + NamespaceField = namespace_field(Meta), 215 215 + [NamespaceField] ++ PidFields ++ Fields; 216 216 + 217 217 + fields(Meta = #{fields := Fields}, _GetPid) -> 218 218 + NamespaceField = namespace_field(Meta), 219 219 + [NamespaceField] ++ Fields; 220 220 + fields(_Meta, _GetPid) -> []. 221 221 + 222 222 + % Get the `namespace` field from the LogEvent metadata() 223 223 + % `unknown` if it isnt present 224 224 + -spec namespace_field(logger:metadata()) -> witness:field(). 225 225 + namespace_field(Meta) -> 226 226 + Domain = maps:get(domain, Meta, [witness, unknown]), 227 227 + Namespace = namespace_from_domain(Domain), 228 228 + witness:string(~"namespace", atom_to_binary(Namespace)). 229 229 + 230 230 + namespace_from_domain([witness, Namespace]) when is_atom(Namespace) -> Namespace; 231 231 + namespace_from_domain(_) -> unknown. 232 232 + 233 233 + report_to_fields(Report) when is_map(Report) -> report_to_fields(maps:to_list(Report)); 234 234 + report_to_fields(Report) when is_list(Report) -> 235 235 + Msg = case lists:keyfind(~"msg", 1, Report) of 236 236 + {_, Found} -> Found; 237 237 + false -> ~"Report" 238 238 + end, 239 239 + ReportWithoutMsg = lists:keydelete(~"msg", 1, Report), 240 240 + Fields = lists:map(fun to_field/1, ReportWithoutMsg), 241 241 + {Msg, Fields}. 242 242 + 243 243 + 244 244 + % Convert a `Report` value into a witness field 245 245 + -spec to_field({any(), any()}) -> witness:field(). 246 246 + 247 247 + to_field({Name, Value}) when is_atom(Name), is_bitstring(Value) -> witness:string(atom_to_binary(Name), Value); 248 248 + to_field({Name, Value}) when is_atom(Name), is_integer(Value) -> witness:int(atom_to_binary(Name), Value); 249 249 + to_field({Name, Value}) when is_atom(Name), is_float(Value) -> witness:float(atom_to_binary(Name), Value); 250 250 + to_field({Name, Value}) when is_atom(Name), is_boolean(Value) -> witness:bool(atom_to_binary(Name), Value); 251 251 + to_field({Name, Value}) when is_atom(Name) -> witness:string(atom_to_binary(Name), gleam@string:inspect(Value)); 252 252 + to_field({Name, Value}) -> witness:string(io_lib:bformat("~p", [Name]), gleam@string:inspect(Value)). 253 253 + 254 254 + % Get metadata from a LogEvent 255 255 + -spec meta(logger:log_event()) -> logger:metadata(). 256 256 + meta(#{meta := Meta}) -> Meta. 257 257 + 258 258 + 259 259 + % Get a short HH:MM:SS timestamp 260 260 + short_timestamp() -> short_timestamp(#{}). 261 261 + 262 262 + -spec short_timestamp(logger:metadata()) -> binary(). 263 263 + short_timestamp(Meta) -> 264 264 + TimeMicros = maps:get(time, Meta, erlang:system_time(microsecond)), 265 265 + {{_Year, _Month, _Day}, {Hour, Min, Sec}} = 266 266 + calendar:system_time_to_local_time(TimeMicros, microsecond), 267 267 + % Format as: 2025-10-11 01:18:16 268 268 + io_lib:bformat("~2..0B:~2..0B:~2..0B", [Hour, Min, Sec]). 269 269 + 270 270 + 271 271 + % Get a long form rfc3339 timestamp 272 272 + rfc_3339_timestamp() -> rfc_3339_timestamp (#{}). 273 273 + 274 274 + -spec rfc_3339_timestamp(logger:metadata()) -> binary(). 275 275 + rfc_3339_timestamp(Meta) -> 276 276 + Time = maps:get(time, Meta, erlang:system_time(microsecond)), 277 277 + calendar:system_time_to_rfc3339(Time, [{return, binary}, {unit, microsecond}]). 278 278 + 279 279 + %% ------------------------------------------------------------------------------ 280 280 + %% logger_handler implementation 281 281 + %% Should only be used for custom witness sinks. 282 282 + %% ------------------------------------------------------------------------------ 283 283 + 284 284 + -spec log(LogEvent, Config) -> nil when 285 285 + LogEvent :: logger:log_event(), 286 286 + Config :: logger_handler:config(). 287 287 + 288 288 + log(LogEvent, #{config := #{handler := Handler}, 289 289 + formatter := {FormatterModule, FormatterConfig} 290 290 + }) when is_function(Handler) -> 291 291 + Formatted = try FormatterModule:format(LogEvent, FormatterConfig) of 292 292 + Form -> Form 293 293 + catch 294 294 + Error:Reason -> format_catch(Error, Reason, LogEvent, FormatterConfig) 295 295 + end, 296 296 + try Handler(Formatted) of 297 297 + nil -> nil 298 298 + catch 299 299 + Err:Reas -> io:fwrite("~ts", 300 300 + [["[WITNESS CUSTOM HANDLER CRASHED: ", 301 301 + atom_to_list(Err), 302 302 + " ", 303 303 + io_lib:format("~p", [Reas]), 304 304 + "]\n" 305 305 + ]]), nil 35 306 end.

+1

.gitignore

Reviewed

··· 7 7 .direnv/ 8 8 .elp 9 9 .elp.build_info 10 10 + testing.log

+41 -2

src/witness.ffi.mjs

Reviewed

··· 1 1 + import { 2 2 + Level$isDebug, 3 3 + Level$isInfo, 4 4 + Level$isNotice, 5 5 + Level$isWarning, 6 6 + Level$isError, 7 7 + Level$isCritical, 8 8 + Level$isAlert, 9 9 + Level$isEmergency 10 10 + } from "./witness.mjs"; 1 11 12 12 + var global_config; 2 13 14 14 + export function get_config(config) { 3 15 4 16 5 17 18 18 + return global_config; 19 19 + } 6 20 21 21 + export function configure(config) { 22 22 + global_config = config 23 23 + } 7 24 25 25 + export function short_timestamp() { 26 26 + return new Date().toLocaleTimeString("en-GB") 27 27 + } 8 28 29 29 + export function iso_8601_timestamp() { 30 30 + return new Date().toISOString() 31 31 + } 9 32 10 10 - export function set_config(config) { 11 11 - global_config = config 33 33 + export function print(message, level) { 34 34 + if(Level$isDebug(level)){ 35 35 + console.debug(message) 36 36 + return undefined 37 37 + } 38 38 + 39 39 + if(Level$isInfo(level) || Level$isNotice(level)) { 40 40 + console.info(message) 41 41 + return undefined 42 42 + } 43 43 + 44 44 + if(Level$isWarning(level)) { 45 45 + console.warn(message) 46 46 + return undefined 47 47 + } 48 48 + 49 49 + console.error(message) 50 50 + return undefined 12 51 }

-64

erlang-logger.md

Reviewed

··· 1 1 - # Erlang logger integration 2 2 - 3 3 - In this I will go over some of the options I have thought of for the 4 4 - outstanding integration of `witness` with the erlang `logger`. 5 5 - 6 6 - ## DIY 7 7 - 8 8 - Add a `witness.erlang_logger` sink which gets the bare log event. 9 9 - Leaving the formatting entirely to the user of the library. 10 10 - 11 11 - ## Basic, single config 12 12 - 13 13 - Add something like `witness.configure(ErlangLoggerConfig)` 14 14 - 15 15 - Where there `LoggerConfig` looks something like: 16 16 - ```gleam 17 17 - LoggerConfig { 18 18 - level: Level 19 19 - format: Format // <- existing format options (Text, Json) 20 20 - destination: Destination 21 21 - } 22 22 - 23 23 - Destination { 24 24 - File(path: String) 25 25 - Stdout 26 26 - } 27 27 - ``` 28 28 - It would be used to configure the erlang `logger`. 29 29 - 30 30 - ## Advanced, multi config 31 31 - 32 32 - Add something like `witness.configure(ErlangLoggerConfig)` 33 33 - 34 34 - Where there `LoggerConfig` looks something like: 35 35 - ```gleam 36 36 - LoggerConfig { 37 37 - sinks: List(SinkConfig) 38 38 - } 39 39 - 40 40 - SinkConfig { 41 41 - level: Level 42 42 - format: Format // <- existing format options (Text, Json) 43 43 - destination: Destination 44 44 - } 45 45 - 46 46 - Destination { 47 47 - File(path: String) 48 48 - Stdout 49 49 - } 50 50 - ``` 51 51 - It would be used to configure the erlang `logger`. 52 52 - 53 53 - I'm imagining an API similar to the following for a common configuration of logging 54 54 - severe things to a file and everything to stdout. 55 55 - ```gleam 56 56 - witness.new() 57 57 - |> witness.with_file(witness.Warning, witness.Json, "./my-app.log") 58 58 - |> witness.with_stdout(witness.Debug, witness.Text) 59 59 - |> witness.configure 60 60 - ``` 61 61 - 62 62 - ## Notes 63 63 - 64 64 - If you have alternate ideas, please let me know.

+78 -17

src/witness.gleam

Reviewed

··· 139 139 140 140 @external(erlang, "witness_ffi", "rfc_3339_timestamp") 141 141 @external(javascript, "./witness.ffi.mjs", "iso_8601_timestamp") 142 142 - fn rfc_3339_date() -> String 142 142 + fn long_date() -> String 143 143 144 144 fn level_to_badge(level: Level) -> String { 145 145 case level { ··· 275 275 /// 276 276 /// `File` handlers use a hash of the path (`witness_file_<hash>`) and `custom` 277 277 /// handlers are indexed (`witness_custom_<index>`). 278 278 + /// 279 279 + /// Your supplied `namespace` will also be turned into an atom! 278 280 /// 279 281 /// Keep in mind that generating too many atoms will result in the atom table 280 282 /// getting filled and causing the entire virtual machine to crash. ··· 284 286 pub fn configure(config: Config) -> Nil 285 287 286 288 pub opaque type Sink { 287 287 - File(level: Level, format: Format, path: String) 289 289 + File(level: Level, format: Format, config: FileConfig) 288 290 Console(level: Level, format: Format) 289 291 Custom(level: Level, format: Format, handler: fn(String) -> Nil) 290 292 } ··· 298 300 /// "ts": "2026-05-28T18:30:40.020522296Z", 299 301 /// "level": "info", 300 302 /// "msg": "Some log message", 303 303 + /// "namespace": "my-application", 301 304 /// "example": "you can add structured data", 302 305 /// "also_bools": true, 303 306 /// "and_floats": 1.23, ··· 308 311 Json 309 312 /// ``` 310 313 /// [INFO] 20:30:40 Some log message 314 314 + /// namespace: my-application 311 315 /// example: you can add structured data 312 316 /// also_bools: True 313 317 /// and_floats: 1.23 ··· 317 321 Text 318 322 } 319 323 320 320 - @target(erlang) 321 321 - /// ----------------------------------------------------------------------------- 322 322 - /// Add a file logger to the logger configuration. Each file logger will get its 323 323 - /// own `logger_std_h` handler added to the `logger` configuration. 324 324 - /// 325 325 - pub fn add_file( 326 326 - config: Config, 327 327 - level: Level, 328 328 - format: Format, 329 329 - path: String, 330 330 - ) -> Config { 331 331 - Config(..config, sinks: [File(level:, format:, path:), ..config.sinks]) 332 332 - } 333 333 - 334 324 /// ----------------------------------------------------------------------------- 335 325 /// Add console logging to your configuration. 336 326 /// ··· 468 458 ) 469 459 Json -> 470 460 format_json([ 471 471 - string("ts", rfc_3339_date()), 461 461 + string("ts", long_date()), 472 462 string("level", level_to_string(level)), 473 463 string("msg", message), 474 464 ..fields ··· 551 541 WBool(name: _, value:) -> name <> string.lowercase(bool.to_string(value)) 552 542 } 553 543 } 544 544 + 545 545 + // ------------------------------------------------------------------------------ 546 546 + // FILE SINK 547 547 + // ------------------------------------------------------------------------------ 548 548 + 549 549 + @target(erlang) 550 550 + /// ----------------------------------------------------------------------------- 551 551 + /// Add a file logger to the logger configuration. Each file logger will get its 552 552 + /// own `logger_std_h` handler added to the `logger` configuration. 553 553 + /// 554 554 + pub fn add_file( 555 555 + config: Config, 556 556 + level: Level, 557 557 + format: Format, 558 558 + file: FileConfig, 559 559 + ) -> Config { 560 560 + Config(..config, sinks: [File(level:, format:, config: file), ..config.sinks]) 561 561 + } 562 562 + 563 563 + @target(erlang) 564 564 + const default_file = FileConfig( 565 565 + path: "witness.log", 566 566 + // 10MB 567 567 + max_bytes: 10_000_000, 568 568 + max_files: 5, 569 569 + compress: False, 570 570 + ) 571 571 + 572 572 + pub opaque type FileConfig { 573 573 + FileConfig(path: String, max_bytes: Int, max_files: Int, compress: Bool) 574 574 + } 575 575 + 576 576 + @target(erlang) 577 577 + /// ----------------------------------------------------------------------------- 578 578 + /// Create a new file logger config. By default it will rotate the file once it 579 579 + /// reaches 10MB, and will keep the last 5. Uncompressed. 580 580 + /// 581 581 + /// See the `file_` functions to configure something else if you need it. 582 582 + /// 583 583 + pub fn new_file(path: String) { 584 584 + FileConfig(..default_file, path:) 585 585 + } 586 586 + 587 587 + @target(erlang) 588 588 + /// ----------------------------------------- 589 589 + /// Configure the maximum file size in Bytes. 590 590 + /// 591 591 + /// Default: 10MB 592 592 + /// 593 593 + pub fn file_size_b(config: FileConfig, size: Int) { 594 594 + FileConfig(..config, max_bytes: size) 595 595 + } 596 596 + 597 597 + @target(erlang) 598 598 + /// --------------------------------- 599 599 + /// Configure how many files to keep. 600 600 + /// 601 601 + /// Default: 5 602 602 + /// 603 603 + pub fn file_keep(config: FileConfig, count: Int) { 604 604 + FileConfig(..config, max_files: count) 605 605 + } 606 606 + 607 607 + @target(erlang) 608 608 + /// ----------------------------------------------------------------------------- 609 609 + /// Enable compression for rotated log files. When a file gets rotated it will be 610 610 + /// compressed with `gzip`, and renamed to `FileName.N.gz` 611 611 + /// 612 612 + pub fn file_compress(config: FileConfig) { 613 613 + FileConfig(..config, compress: True) 614 614 + }

+61 -21

README.md

Reviewed

··· 4 4 [](https://witness.hexdocs.pm/) 5 5 6 6 ```sh 7 7 - gleam add witness@1 logging@1 7 7 + gleam add witness@1 8 8 ``` 9 9 ```gleam 10 10 import gleam/io ··· 14 14 configure_logging() 15 15 16 16 // log a message 17 17 - witness.this(witness.Info, "Some log message", [ 17 17 + witness.this(witness.Warning, "Some log message", [ 18 18 witness.string("example", "you can add structured data"), 19 19 witness.bool("also_bools", True), 20 20 witness.float("and_floats", 1.23), ··· 26 26 /// 27 27 fn configure_logging() { 28 28 // create a new config 29 29 - witness.empty_config() 30 30 - // log formatted text to stdout 31 31 - |> witness.with_sink(witness.Text, fn(level, message) { 32 32 - io.println(witness.level_to_badge(level) <> ": " <> message) 29 29 + witness.new("witness-dev") 30 30 + |> witness.with_global_fields([ 31 31 + witness.string( 32 32 + "my-global-field", 33 33 + "something i really need logged everywhere", 34 34 + ), 35 35 + ]) 36 36 + |> witness.with_console(witness.Debug, witness.Text) 37 37 + |> witness.add_file( // <- erlang only 38 38 + witness.Warning, 39 39 + witness.Json, 40 40 + witness.new_file("testing.log"), 41 41 + ) 42 42 + |> witness.add_custom(witness.Debug, witness.Json, fn(message) { 43 43 + // Whatever you do in here has to be executed by the calling process 44 44 + // i.e. whoever ran `witness.this`, so try to keep processing low. 45 45 + // 46 46 + // On erlang you could, for example, `process.send` the log event 47 47 + // to a handler process somewhere in your supervision tree. 48 48 + io.println("Hello from my custom handler!\n" <> message) 33 49 }) 34 34 - // log as json 35 35 - |> witness.with_sink(witness.Json, fn(_, message) { 36 36 - // ideally you'd log this to a file using, for example, the erlang logger 37 37 - io.println(message) 38 38 - }) 39 39 - // apply this config globally 40 40 - |> witness.set_config() 50 50 + |> witness.configure 41 51 } 42 52 ``` 43 43 - Will log this json line: 53 53 + Will log this text to console: 54 54 + ```plain 55 55 + [WARN] 16:06:45: Some log message 56 56 + namespace: witness-dev 57 57 + pid*: <0.83.0> 58 58 + my-global-field: somethign i really need globally 59 59 + example: you can add structured data 60 60 + also_bools: True 61 61 + and_floats: 1.23 62 62 + ints_as_well: 3 44 63 ``` 45 45 - {"timestamp":"2026-07-22T17:13:17.100815963Z","level":"info","message":"Some log message","example":"you can add structured data","also_bools":true,"and_floats":1.23,"ints_as_well":3} 64 64 + and this json line to `io.println`, from the custom handler: 65 65 + ```plain 66 66 + Hello from my custom handler! 67 67 + {"ts":"2026-07-26T14:06:45.295Z","level":"warning","msg":"Some log message","namespace":"witness-dev","my-global-field":"somethign i really need globally","example":"you can add structured data","also_bools":true,"and_floats":1.23,"ints_as_well":3} 46 68 ``` 47 47 - And this text to the console: 69 69 + And this json line to `testing.log`: 70 70 + ```json 71 71 + {"ts":"2026-07-26T16:09:28.963532+02:00","level":"warning","msg":"Some log message","namespace":"witness-dev","my-global-field":"something i really need logged everywhere","example":"you can add structured data","also_bools":true,"and_floats":1.23,"ints_as_well":3} 48 72 ``` 49 49 - [INFO]: 19:13:17 Some log message 50 50 - example: you can add structured data 51 51 - also_bools: True 52 52 - and_floats: 1.23 53 53 - ints_as_well: 3 73 73 + 74 74 + ### Notes 75 75 + 76 76 + The file sink is only available on the erlang target. Since it uses `logger_std_h` 77 77 + to do the actual writing to file. And the javascript target may not even have a file 78 78 + to log to. 79 79 + 80 80 + #### Erlang 81 81 + 82 82 + The `console` and `custom` handlers, which are configured with `witness.Debug`, 83 83 + also logged the `pid*` of the calling process (i.e. the process that called `witness.this`). 84 84 + If they were registered under a name, that name would also show up as `registered_name*`. 85 85 + 86 86 + All messages logged by witness have a domain of `domain => [witness, <namespace>]` so they may 87 87 + be filtered out entirely like this: 88 88 + ```erl 89 89 + filters => [{domain, {fun logger_filters:domain/2, {stop, sub, [witness]}}}] 90 90 + ``` 91 91 + or only specific namespaces like this: 92 92 + ```erl 93 93 + filters => [{domain, {fun logger_filters:domain/2, {stop, sub, [witness, <namespace>]}}}] 54 94 ``` 55 95 56 96 Further documentation can be found at <https://witness.hexdocs.pm>.

-3

gleam.toml

Reviewed

··· 14 14 15 15 [dependencies] 16 16 gleam_stdlib = ">= 1.0.0 and < 2.0.0" 17 17 - gleam_json = ">= 3.1.0 and < 4.0.0" 18 18 - gleam_time = ">= 1.8.0 and < 2.0.0" 19 17 20 18 [dev-dependencies] 21 19 gleeunit = ">= 1.0.0 and < 2.0.0" 22 22 - gleam_erlang = ">= 1.3.0 and < 2.0.0"

+17 -1

CHANGELOG.md

Reviewed

··· 1 1 + # 3.0.0 2 2 + - Integrate with the erlang logger. All logs that go through the erlang logger will now also get formatted. 3 3 + - Added `file` sink for the erlang target. 4 4 + - Added `new_file`, `file_compress`, `file_keep` and `file_size_b` to configure the file sink. 5 5 + - Added `with_console`, `add_file` and `add_custom` to configure sinks. 6 6 + - Dropped `gleam_time`, `gleam_json` and `gleam_erlang` dependencies 7 7 + - Replaced `persistent_term` uses on erlang with `ets`. 8 8 + 9 9 + # Breaking changes 10 10 + - Removed `default_config` in favor of `new`. 11 11 + - Removed `empty_config` in favor of `new`. 12 12 + - Removed `with_sink` in favor of `with_console`, `add_custom` and `add_file`. 13 13 + - Renamed `set_config` to `configure`. 14 14 + 15 15 + --- 16 16 + 1 17 # 2.0.0 2 18 - Add support for javascript 3 3 - - Drop dependency on `logging` 19 19 + - Dropped `logging` dependency 4 20 5 21 # Breaking changes 6 22 - `logging.Level` was replaced with `witness.Level`