Initial implementation.

.gitignore

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+# ignore vim swap files
+.*.sw?
+
+# ignore built binary
+/slfmt

slfmt.nimble

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+# Package
+
+version       = "0.1.0"
+author        = "Jonathan Bernard"
+description   = "Small utility to pretty-print strucutured logs."
+license       = "MIT"
+srcDir        = "src"
+bin           = @["slfmt"]
+
+
+# Dependencies
+
+requires "nim >= 2.2.0"
+requires "timeutils"

src/slfmt.nim

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+import std/[json, sequtils, streams, strutils, terminal, times]
+import timeutils
+#import docopt
+
+const VERSION = "0.1.0"
+
+# const USAGE = """Usage:
+#   slfmt
+#
+# Options:
+#
+#   -h, --help            Print this usage and help information
+
+const fieldDisplayOrder = @[
+  "scope", "level", "ts", "code", "sid", "sub", "msg", "err", "stack", "method", "args"]
+
+func decorate(
+    s: string,
+    fg = fgDefault,
+    style: set[Style] = {}): string =
+
+  result = ""
+
+  if style != {}:
+    result &= toSeq(items(style)).mapIt(ansiStyleCode(it)).join("")
+
+  if fg != fgDefault: result &= ansiForegroundColorCode(fg)
+
+  result &= s & ansiResetCode
+
+
+proc formatField(name: string, value: JsonNode): string =
+  result = decorate(name, fgCyan) & ":" & " ".repeat(max(1, 10 - name.len))
+
+  var strVal: string = ""
+  case name:
+    of "ts":
+      let dt = parseIso8601(value.getStr)
+      strVal = decorate(dt.local.formatIso8601 & " (local)  ", fgBlue, {styleBright}) &
+        dt.utc.formatIso8601 & " (UTC)"
+    of "sid", "sub": strVal = decorate(value.getStr, fgGreen)
+    of "err": strVal = decorate(value.getStr, fgRed)
+    of "msg": strVal = decorate(value.getStr, fgYellow)
+    of "stack": strVal = decorate(value.getStr, fgBlack, {styleBright})
+    else: strVal = pretty(value)
+
+  let valLines = splitLines(strVal)
+  if name.len > 10 or strVal.len + 16 > terminalWidth() or valLines.len > 1:
+    result &= "\n" & valLines.mapIt("  " & it).join("\n") & "\n"
+  else: result &= strVal & "\n"
+
+proc prettyPrintFormat(logLine: string): string =
+  try:
+    var logJson = parseJson(logLine)
+
+    result = '-'.repeat(terminalWidth())
+
+    # Print the known fields in order first
+    for f in fieldDisplayOrder:
+      if logJson.hasKey(f):
+        result &= formatField(f, logJson[f])
+        logJson.delete(f)
+
+    # Print the rest of the fields
+    for (key, val) in pairs(logJson): result &= formatField(key, val)
+
+    result &= "\n"
+
+  except ValueError, JsonParsingError:
+    result = logLine
+
+when isMainModule:
+  try:
+    var line: string = ""
+    let sin = newFileStream(stdin)
+    while(sin.readLine(line)): stdout.writeLine(prettyPrintFormat(line))
+  except:
+    stderr.writeLine("slfmt - FATAL: " & getCurrentExceptionMsg())
+    stderr.writeLine(getCurrentException().getStackTrace())
+    quit(QuitFailure)