feat: add json parser

src/lib/json.lua

@@ -0,0 +1,202 @@
+local json = {}
+
+json.null = {}
+
+local function trim(str)
+    return string.gsub(str, "^%s+", "")
+end
+
+local function startswith(str, prefix)
+    return str:sub(1, prefix:len()) == prefix
+end
+
+local function endswith(str, suffix)
+    return str:sub(str:len() - suffix:len() + 1) == suffix
+end
+
+local function errFactory(prefix)
+    return function (message)
+        print(prefix .. ": " .. message)
+    end
+end
+
+local function parseObj(data)
+    local printErr = errFactory("Error while parsing object")
+    local obj = {}
+    local c = ""
+    local key = ""
+    local keyEnd, value
+    local l = -1
+    while true do
+        if data:len() == l then
+            printErr("infinite loop")
+            return data, nil
+        end
+        l = data:len()
+        data = trim(data)
+        if data:len() == 0 then
+            printErr("incomplete object")
+            return data, nil
+        end
+        c = data:sub(1, 1)
+        data = data:sub(2)
+        if c == "}" then
+            break
+        end
+        if c ~= '"' then
+            printErr("key must be a string")
+            return data, nil
+        end
+        keyEnd = data:find('"')
+        if not keyEnd then
+            printErr("unclosed key")
+            return data, nil
+        end
+        key = data:sub(1, keyEnd - 1)
+        data = trim(data:sub(keyEnd + 1))
+        c = data:sub(1, 1)
+        if c ~= ":" then
+            printErr("missing colon after key")
+            return data, nil
+        end
+        data = data:sub(2)
+        data, value = json.parse(data)
+        if value == nil then
+            printErr("malformed value")
+            return data, nil
+        end
+        data = trim(data)
+        obj[key] = value
+
+        c = data:sub(1, 1)
+        if c == "," then
+            data = trim(data:sub(2))
+        else
+            if data:sub(1, 1) ~= "}" then
+                printErr("missing comma")
+                return data, nil
+            end
+            data = trim(data:sub(2))
+            break
+        end
+    end
+    return data, obj
+end
+
+local function parseList(data)
+    local printErr = errFactory("Error while parsing array")
+    local list = {}
+    local c
+    local value
+    while true do
+        data = trim(data)
+        if data:len() == 0 then
+            printErr("incomplete array")
+            return data, nil
+        end
+        c = data:sub(1, 1)
+        if c == "]" then
+            data = data:sub(2)
+            break
+        end
+        data, value = json.parse(data)
+        if value == nil then
+            printErr("malformed value")
+            return data, nil
+        end
+        data = trim(data)
+        list[#list + 1] = value
+
+        c = data:sub(1, 1)
+        if c == "," then
+            data = trim(data:sub(2))
+        else
+            if data:sub(1, 1) ~= "]" then
+                printErr("missing comma")
+                return data, nil
+            end
+            data = trim(data:sub(2))
+            break
+        end
+    end
+    return data, list
+end
+
+local function parseString(data)
+    local printErr = errFactory("Error while parsing string")
+    local str = ""
+    local c = ""
+    local escape = false
+    local escapeMap = {
+        b = "\b",
+        f = "\f",
+        n = "\n",
+        r = "\r",
+        t = "\t"
+    }
+
+    while data:len() ~= 0 do
+        c = data:sub(1, 1)
+        data = data:sub(2)
+        if c == '"' and not escape then
+            return data, str
+        end
+        if escape then
+            str = str .. (escapeMap[c] or c)
+            escape = false
+        else
+            if c == "\\" then
+                escape = true
+            else
+                str = str .. c
+            end
+        end
+    end
+    printErr("unclosed string")
+    return data, nil
+end
+
+function json.parse(data)
+    data = data:gsub("^%s+", "")
+    if data:len() == 0 then
+        printError("Empty JSON")
+        return data, nil
+    end
+    local c = data:sub(1, 1)
+    local data2 = data:sub(2)
+    if c == "{" then
+        return parseObj(data2)
+    elseif c == "[" then
+        return parseList(data2)
+    elseif startswith(data, "true") then
+        return data:sub(5), true
+    elseif startswith(data, "false") then
+        return data:sub(6), false
+    elseif startswith(data, "null") then
+        return data:sub(5), json.null
+    elseif c == '"' then
+        return parseString(data2)
+    end
+    
+    local m = data:match("^-?%d+%.?%d*[eE]?[+-]?%d*")
+    if m then
+        data = data:sub(m:len() + 1)
+        return data, tonumber(m)
+    else
+        printError("Malformed JSON")
+        return data, nil
+    end
+end
+
+function json.loads(data)
+    local remaining, res = json.parse(data)
+    if res == nil then
+        printError("An error occured")
+    end
+    if remaining:len() ~= 0 then
+        print("Extra characters: " .. remaining)
+    end
+    return res
+end
+
+return json