jfkinslow · July 18, 2021 01:11 · Oct 28, 2014 · Oct 28, 2014 · Oct 28, 2014 · Oct 15, 2014
diff --git a/json.lua b/json.lua
@@ -154,26 +154,26 @@ function json.parse(str, pos, end_delim)
   local pos = pos + #str:match('^%s*', pos)  -- Skip whitespace.
   local first = str:sub(pos, pos)
   if first == '{' then  -- Parse an object.
-    local obj, key, did_find_delim = {}, true, true
+    local obj, key, delim_found = {}, true, true
     pos = pos + 1
-    while did_find_delim do
+    while true do
       key, pos = json.parse(str, pos, '}')
-      if key then
-        pos = skip_delim(str, pos, ':', true)  -- true -> error if missing.
-        obj[key], pos = json.parse(str, pos)
-      end
-      pos, did_find_delim = skip_delim(str, pos, ',')
+      if key == nil then return obj, pos end
+      if not delim_found then error('Comma missing between object items.') end
+      pos = skip_delim(str, pos, ':', true)  -- true -> error if missing.
+      obj[key], pos = json.parse(str, pos)
+      pos, delim_found = skip_delim(str, pos, ',')
     end
-    return obj, pos
   elseif first == '[' then  -- Parse an array.
-    local arr, val, did_find_delim = {}, true, true
+    local arr, val, delim_found = {}, true, true
     pos = pos + 1
-    while did_find_delim do
+    while true do
       val, pos = json.parse(str, pos, ']')
-      if val then arr[#arr + 1] = val end
-      pos, did_find_delim = skip_delim(str, pos, ',')
+      if val == nil then return arr, pos end
+      if not delim_found then error('Comma missing between array items.') end
+      arr[#arr + 1] = val
+      pos, delim_found = skip_delim(str, pos, ',')
     end
-    return arr, pos
   elseif first == '"' then  -- Parse a string.
     return parse_str_val(str, pos + 1)
   elseif first == '-' or first:match('%d') then  -- Parse a number.

diff --git a/json.lua b/json.lua
@@ -33,7 +33,7 @@ as arbitrary a Lua object as json is capable of expressing.
 This function parses json, with the exception that it does not pay attention to
 \u-escaped unicode code points in strings.
 
-It is difficult to Lua to return null as a value. In order to prevent the loss
+It is difficult for Lua to return null as a value. In order to prevent the loss
 of keys with a null value in a json string, this function uses the one-off
 table value json.null (which is just an empty table) to indicate null values.
 This way you can check if a value is null with the conditional

diff --git a/json.lua b/json.lua
@@ -1,41 +1,56 @@
--- json.lua
---
--- A function to stringify a Lua object into json.
---
--- This expects the following to be true of any tables
--- being encoded:
---  * They only have string or number keys.
---    Number keys must be represented as strings in json;
---    this is part of the json spec.
---  * They are not recursive. Such a structure cannot be
---    specified in json.
---
--- A Lua table is considered to be an array if and only if
--- its set of keys is a consecutive sequence of positive
--- integers starting at 1. Arrays are encoded like so:
--- [2, 3, false, "hi"]. Any other type of Lua table is
--- encoded as a json object, encoded like so:
--- {"key1": 2, "key2": false}.
---
--- Because the Lua nil value cannot be a key, and as a
--- table value is considerd equivalent to a missing key,
--- there is no way to express the json "null" value in a
--- Lua table. The only way this will output "null" is if
--- your entire input obj is nil itself.
---
--- An empty Lua table, {}, could be considered either a
--- json object or array - it's an ambiguous edge case.
--- We choose to treat this as an object as it is the
--- more general type.
---
--- To be clear, none of the above considerations is a
--- limitation of this code. Rather, it is what we get when
--- we completely observe the json specification for
--- as arbitrary a Lua object as json is capable of
--- expressing.
---
-
-function kind_of(obj)
+--[[ json.lua
+
+A compact pure-Lua JSON library.
+The main functions are: json.stringify, json.parse.
+
+## json.stringify:
+
+This expects the following to be true of any tables being encoded:
+ * They only have string or number keys. Number keys must be represented as
+   strings in json; this is part of the json spec.
+ * They are not recursive. Such a structure cannot be specified in json.
+
+A Lua table is considered to be an array if and only if its set of keys is a
+consecutive sequence of positive integers starting at 1. Arrays are encoded like
+so: `[2, 3, false, "hi"]`. Any other type of Lua table is encoded as a json
+object, encoded like so: `{"key1": 2, "key2": false}`.
+
+Because the Lua nil value cannot be a key, and as a table value is considerd
+equivalent to a missing key, there is no way to express the json "null" value in
+a Lua table. The only way this will output "null" is if your entire input obj is
+nil itself.
+
+An empty Lua table, {}, could be considered either a json object or array -
+it's an ambiguous edge case. We choose to treat this as an object as it is the
+more general type.
+
+To be clear, none of the above considerations is a limitation of this code.
+Rather, it is what we get when we completely observe the json specification for
+as arbitrary a Lua object as json is capable of expressing.
+
+## json.parse:
+
+This function parses json, with the exception that it does not pay attention to
+\u-escaped unicode code points in strings.
+
+It is difficult to Lua to return null as a value. In order to prevent the loss
+of keys with a null value in a json string, this function uses the one-off
+table value json.null (which is just an empty table) to indicate null values.
+This way you can check if a value is null with the conditional
+`val == json.null`.
+
+If you have control over the data and are using Lua, I would recommend just
+avoiding null values in your data to begin with.
+
+--]]
+
+
+local json = {}
+
+
+-- Internal functions.
+
+local function kind_of(obj)
   if type(obj) ~= 'table' then return type(obj) end
   local i = 1
   for _ in pairs(obj) do
@@ -44,7 +59,7 @@ function kind_of(obj)
   if i == 1 then return 'table' else return 'array' end
 end
 
-function escape_str(s)
+local function escape_str(s)
   local in_char  = {'\\', '"', '/', '\b', '\f', '\n', '\r', '\t'}
   local out_char = {'\\', '"', '/',  'b',  'f',  'n',  'r',  't'}
   for i, c in ipairs(in_char) do
@@ -53,25 +68,67 @@ function escape_str(s)
   return s
 end
 
-function json_stringify(obj, as_key)
+-- Returns pos, did_find; there are two cases:
+-- 1. Delimiter found: pos = pos after leading space + delim; did_find = true.
+-- 2. Delimiter not found: pos = pos after leading space;     did_find = false.
+-- This throws an error if err_if_missing is true and the delim is not found.
+local function skip_delim(str, pos, delim, err_if_missing)
+  pos = pos + #str:match('^%s*', pos)
+  if str:sub(pos, pos) ~= delim then
+    if err_if_missing then
+      error('Expected ' .. delim .. ' near position ' .. pos)
+    end
+    return pos, false
+  end
+  return pos + 1, true
+end
+
+-- Expects the given pos to be the first character after the opening quote.
+-- Returns val, pos; the returned pos is after the closing quote character.
+local function parse_str_val(str, pos, val)
+  val = val or ''
+  local early_end_error = 'End of input found while parsing string.'
+  if pos > #str then error(early_end_error) end
+  local c = str:sub(pos, pos)
+  if c == '"'  then return val, pos + 1 end
+  if c ~= '\\' then return parse_str_val(str, pos + 1, val .. c) end
+  -- We must have a \ character.
+  local esc_map = {b = '\b', f = '\f', n = '\n', r = '\r', t = '\t'}
+  local nextc = str:sub(pos + 1, pos + 1)
+  if not nextc then error(early_end_error) end
+  return parse_str_val(str, pos + 2, val .. (esc_map[nextc] or nextc))
+end
+
+-- Returns val, pos; the returned pos is after the number's final character.
+local function parse_num_val(str, pos)
+  local num_str = str:match('^-?%d+%.?%d*[eE]?[+-]?%d*', pos)
+  local val = tonumber(num_str)
+  if not val then error('Error parsing number at position ' .. pos .. '.') end
+  return val, pos + #num_str
+end
+
+
+-- Public values and functions.
+
+function json.stringify(obj, as_key)
   local s = {}  -- We'll build the string as an array of strings to be concatenated.
   local kind = kind_of(obj)  -- This is 'array' if it's an array or type(obj) otherwise.
   if kind == 'array' then
     if as_key then error('Can\'t encode array as key.') end
     s[#s + 1] = '['
     for i, val in ipairs(obj) do
       if i > 1 then s[#s + 1] = ', ' end
-      s[#s + 1] = json_stringify(val)
+      s[#s + 1] = json.stringify(val)
     end
     s[#s + 1] = ']'
   elseif kind == 'table' then
     if as_key then error('Can\'t encode table as key.') end
     s[#s + 1] = '{'
     for k, v in pairs(obj) do
       if #s > 1 then s[#s + 1] = ', ' end
-      s[#s + 1] = json_stringify(k, true)
+      s[#s + 1] = json.stringify(k, true)
       s[#s + 1] = ':'
-      s[#s + 1] = json_stringify(v)
+      s[#s + 1] = json.stringify(v)
     end
     s[#s + 1] = '}'
   elseif kind == 'string' then
@@ -89,3 +146,49 @@ function json_stringify(obj, as_key)
   return table.concat(s)
 end
 
+json.null = {}  -- This is a one-off table to represent the null value.
+
+function json.parse(str, pos, end_delim)
+  pos = pos or 1
+  if pos > #str then error('Reached unexpected end of input.') end
+  local pos = pos + #str:match('^%s*', pos)  -- Skip whitespace.
+  local first = str:sub(pos, pos)
+  if first == '{' then  -- Parse an object.
+    local obj, key, did_find_delim = {}, true, true
+    pos = pos + 1
+    while did_find_delim do
+      key, pos = json.parse(str, pos, '}')
+      if key then
+        pos = skip_delim(str, pos, ':', true)  -- true -> error if missing.
+        obj[key], pos = json.parse(str, pos)
+      end
+      pos, did_find_delim = skip_delim(str, pos, ',')
+    end
+    return obj, pos
+  elseif first == '[' then  -- Parse an array.
+    local arr, val, did_find_delim = {}, true, true
+    pos = pos + 1
+    while did_find_delim do
+      val, pos = json.parse(str, pos, ']')
+      if val then arr[#arr + 1] = val end
+      pos, did_find_delim = skip_delim(str, pos, ',')
+    end
+    return arr, pos
+  elseif first == '"' then  -- Parse a string.
+    return parse_str_val(str, pos + 1)
+  elseif first == '-' or first:match('%d') then  -- Parse a number.
+    return parse_num_val(str, pos)
+  elseif first == end_delim then  -- End of an object or array.
+    return nil, pos + 1
+  else  -- Parse true, false, or null.
+    local literals = {['true'] = true, ['false'] = false, ['null'] = json.null}
+    for lit_str, lit_val in pairs(literals) do
+      local lit_end = pos + #lit_str - 1
+      if str:sub(pos, lit_end) == lit_str then return lit_val, lit_end + 1 end
+    end
+    local pos_info_str = 'position ' .. pos .. ': ' .. str:sub(pos, pos + 10)
+    error('Invalid json syntax starting at ' .. pos_info_str)
+  end
+end
+
+return json
diff --git a/json.lua b/json.lua
@@ -0,0 +1,91 @@
+-- json.lua
+--
+-- A function to stringify a Lua object into json.
+--
+-- This expects the following to be true of any tables
+-- being encoded:
+--  * They only have string or number keys.
+--    Number keys must be represented as strings in json;
+--    this is part of the json spec.
+--  * They are not recursive. Such a structure cannot be
+--    specified in json.
+--
+-- A Lua table is considered to be an array if and only if
+-- its set of keys is a consecutive sequence of positive
+-- integers starting at 1. Arrays are encoded like so:
+-- [2, 3, false, "hi"]. Any other type of Lua table is
+-- encoded as a json object, encoded like so:
+-- {"key1": 2, "key2": false}.
+--
+-- Because the Lua nil value cannot be a key, and as a
+-- table value is considerd equivalent to a missing key,
+-- there is no way to express the json "null" value in a
+-- Lua table. The only way this will output "null" is if
+-- your entire input obj is nil itself.
+--
+-- An empty Lua table, {}, could be considered either a
+-- json object or array - it's an ambiguous edge case.
+-- We choose to treat this as an object as it is the
+-- more general type.
+--
+-- To be clear, none of the above considerations is a
+-- limitation of this code. Rather, it is what we get when
+-- we completely observe the json specification for
+-- as arbitrary a Lua object as json is capable of
+-- expressing.
+--
+
+function kind_of(obj)
+  if type(obj) ~= 'table' then return type(obj) end
+  local i = 1
+  for _ in pairs(obj) do
+    if obj[i] ~= nil then i = i + 1 else return 'table' end
+  end
+  if i == 1 then return 'table' else return 'array' end
+end
+
+function escape_str(s)
+  local in_char  = {'\\', '"', '/', '\b', '\f', '\n', '\r', '\t'}
+  local out_char = {'\\', '"', '/',  'b',  'f',  'n',  'r',  't'}
+  for i, c in ipairs(in_char) do
+    s = s:gsub(c, '\\' .. out_char[i])
+  end
+  return s
+end
+
+function json_stringify(obj, as_key)
+  local s = {}  -- We'll build the string as an array of strings to be concatenated.
+  local kind = kind_of(obj)  -- This is 'array' if it's an array or type(obj) otherwise.
+  if kind == 'array' then
+    if as_key then error('Can\'t encode array as key.') end
+    s[#s + 1] = '['
+    for i, val in ipairs(obj) do
+      if i > 1 then s[#s + 1] = ', ' end
+      s[#s + 1] = json_stringify(val)
+    end
+    s[#s + 1] = ']'
+  elseif kind == 'table' then
+    if as_key then error('Can\'t encode table as key.') end
+    s[#s + 1] = '{'
+    for k, v in pairs(obj) do
+      if #s > 1 then s[#s + 1] = ', ' end
+      s[#s + 1] = json_stringify(k, true)
+      s[#s + 1] = ':'
+      s[#s + 1] = json_stringify(v)
+    end
+    s[#s + 1] = '}'
+  elseif kind == 'string' then
+    return '"' .. escape_str(obj) .. '"'
+  elseif kind == 'number' then
+    if as_key then return '"' .. tostring(obj) .. '"' end
+    return tostring(obj)
+  elseif kind == 'boolean' then
+    return tostring(obj)
+  elseif kind == 'nil' then
+    return 'null'
+  else
+    error('Unjsonifiable type: ' .. kind .. '.')
+  end
+  return table.concat(s)
+end
+
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