string: introduce string.strip

* Add support of string.strip, string.lstrip, string.rstrip

Closes #2785

src/lua/string.lua

@@ -292,6 +292,28 @@ local function string_hex(inp)
     return ffi.string(res, len)
 end
 
+local function string_strip(inp)
+    if type(inp) ~= 'string' then
+        error(err_string_arg:format(1, "string.strip", 'string', type(inp)), 2)
+    end
+    return (string.gsub(inp, "^%s*(.-)%s*$", "%1"))
+end
+
+local function string_lstrip(inp)
+    if type(inp) ~= 'string' then
+        error(err_string_arg:format(1, "string.lstrip", 'string', type(inp)), 2)
+    end
+    return (string.gsub(inp, "^%s*(.-)", "%1"))
+end
+
+local function string_rstrip(inp)
+    if type(inp) ~= 'string' then
+        error(err_string_arg:format(1, "string.rstrip", 'string', type(inp)), 2)
+    end
+    return (string.gsub(inp, "(.-)%s*$", "%1"))
+end
+
+
 -- It'll automatically set string methods, too.
 local string = require('string')
 string.split      = string_split
@@ -301,3 +323,6 @@ string.center     = string_center
 string.startswith = string_startswith
 string.endswith   = string_endswith
 string.hex        = string_hex
+string.strip      = string_strip
+string.lstrip      = string_lstrip
+string.rstrip      = string_rstrip

test/app-tap/string.test.lua

@@ -3,7 +3,7 @@
 local tap = require('tap')
 local test = tap.test("string extensions")
 
-test:plan(4)
+test:plan(5)
 
 test:test("split", function(test)
     test:plan(10)
@@ -114,4 +114,18 @@ test:test("hex", function(test)
     test:is(string.hex(""), "", "hex empty string")
 end)
 
+test:test("strip", function(test)
+    test:plan(6)
+    local str = "  hello hello "
+    test:is(string.len(string.strip(str)), 11, "strip")
+    test:is(string.len(string.lstrip(str)), 12, "lstrip")
+    test:is(string.len(string.rstrip(str)), 13, "rstrip")
+    local _, err = pcall(string.strip, 12)
+    test:ok(err and err:match("%(string expected, got number%)"))
+    _, err = pcall(string.lstrip, 12)
+    test:ok(err and err:match("%(string expected, got number%)"))
+    _, err = pcall(string.rstrip, 12)
+    test:ok(err and err:match("%(string expected, got number%)"))
+end )
+
 os.exit(test:check() == true and 0 or -1)