Initial JSON serializer

json_serialization.nim

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+import json_serialization/[reader, writer]
+export reader, writer
+

json_serialization.nimble

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+mode = ScriptMode.Verbose
+
+packageName   = "json_serialization"
+version       = "0.1.0"
+author        = "Status Research & Development GmbH"
+description   = "JSON serialization without relying on run-time type information"
+license       = "Apache License 2.0"
+skipDirs      = @["tests"]
+
+requires "nim >= 0.17.0",
+         "ranges"
+
+proc configForTests() =
+  --hints: off
+  --debuginfo
+  --path: "."
+  --run
+
+task test, "run tests":
+  configForTests()
+  setCommand "c", "tests/all.nim"
+

json_serialization/writer.nim

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+import
+  typetraits, serialization/streams
+
+type
+  JsonWriterState = enum
+    RecordExpected
+    RecordStarted
+    AfterField
+
+  JsonWriter*[Stream] = object
+    stream*: Stream
+    hasTypeAnnotations: bool
+    hasPrettyOutput*: bool # read-only
+    nestingLevel*: int     # read-only
+    state: JsonWriterState
+
+  StringJsonWriter* = JsonWriter[StringStream]
+
+proc init*(T: type JsonWriter, pretty = false, typeAnnotations = false): T =
+  init result.stream
+  result.hasPrettyOutput = pretty
+  result.hasTypeAnnotations = typeAnnotations
+  result.nestingLevel = if pretty: 0 else: -1
+  result.state = RecordExpected
+
+proc writeImpl(w: var JsonWriter, value: auto)
+
+template writeValue*(w: var JsonWriter, v: auto) =
+  writeImpl(w, v)
+
+proc beginRecord*(w: var JsonWriter, T: type)
+proc beginRecord*(w: var JsonWriter)
+
+template indent(w: var JsonWriter) =
+  for i in 0 ..< w.nestingLevel:
+    w.stream.append ' '
+
+proc writeFieldName*(w: var JsonWriter, name: string) =
+  # this is implemented as a separate proc in order to
+  # keep the code bloat from `writeField` to a minimum
+  assert w.state != RecordExpected
+
+  if w.state == AfterField:
+    w.stream.append ','
+
+  if w.hasPrettyOutput:
+    w.stream.append '\n'
+
+  w.indent()
+
+  w.stream.append '"'
+  w.stream.append name
+  w.stream.append '"'
+  w.stream.append ':'
+  if w.hasPrettyOutput: w.stream.append ' '
+
+proc writeField*(w: var JsonWriter, name: string, value: auto) =
+  mixin writeValue
+
+  w.writeFieldName(name)
+
+  w.state = RecordExpected
+  w.writeValue(value)
+
+  w.state = AfterField
+
+proc beginRecord*(w: var JsonWriter) =
+  assert w.state == RecordExpected
+
+  w.stream.append '{'
+  if w.hasPrettyOutput:
+    w.nestingLevel += 2
+
+  w.state = RecordStarted
+
+proc beginRecord*(w: var JsonWriter, T: type) =
+  w.beginRecord()
+  if w.hasTypeAnnotations: w.writeField("$type", typetraits.name(T))
+
+proc endRecord*(w: var JsonWriter) =
+  assert w.state != RecordExpected
+
+  if w.hasPrettyOutput:
+    w.stream.append '\n'
+    w.nestingLevel -= 2
+    w.indent()
+
+  w.stream.append '}'
+  w.state = RecordExpected
+
+proc writeArray[T](w: var JsonWriter, elements: openarray[T]) =
+  mixin writeValue
+
+  w.stream.append '['
+  for i, e in elements:
+    if i != 0: w.stream.append ','
+    w.state = RecordExpected
+    w.writeValue(e)
+  w.stream.append ']'
+
+proc writeImpl(w: var JsonWriter, value: auto) =
+  template addChar(c) =
+    w.stream.append c
+
+  when value is string:
+    addChar '"'
+
+    template addPrefixSlash(c) =
+      addChar '\\'
+      addChar c
+
+    for c in value:
+      case c
+      of '\L': addPrefixSlash 'n'
+      of '\b': addPrefixSlash 'b'
+      of '\f': addPrefixSlash 'f'
+      of '\t': addPrefixSlash 't'
+      of '\r': addPrefixSlash 'r'
+      of '"' : addPrefixSlash '\"'
+      of '\0'..'\7':
+        w.stream.append "\\u000"
+        w.stream.append char(ord('0') + ord(c))
+      of '\14'..'\31':
+        w.stream.append "\\u00"
+        # TODO: Should this really use a decimal representation?
+        # Or perhaps $ord(c) returns hex?
+        # This is potentially a bug in Nim's json module.
+        # In any case, we can call appendNumber here.
+        w.stream.append $ord(c)
+      of '\\': addPrefixSlash '\\'
+      else: addChar c
+
+    addChar '"'
+
+  elif value is bool:
+    w.stream.append if value: "true" else: "false"
+  elif value is enum:
+    w.stream.appendNumber ord(value)
+  elif value is SomeInteger:
+    w.stream.appendNumber value
+  elif value is SomeFloat:
+    w.stream.append $value
+  elif value is (seq or array):
+    w.writeArray(value)
+  elif value is (object or tuple):
+    w.beginRecord(type(value))
+    # TODO: this won't handle case objects
+    # introduce and use `value.deserializePairs(k, v):`
+    for k, v in value.fieldPairs:
+      w.writeField(k, v)
+    w.endRecord()
+  else:
+    const typeName = typetraits.name(value.type)
+    {.error: "Failed to convert to JSON an unsupported type: " & typeName.}
+
+template getOutput*(w: JsonWriter): auto =
+  w.stream.getOutput
+