Add variable expansion and design doc

third_party/golang/expansion/expand.go

+package expansion
+
+const (
+	operator        = '$'
+	referenceOpener = '('
+	referenceCloser = ')'
+)
+
+// syntaxWrap returns the input string wrapped the expansion syntax.
+func syntaxWrap(input string) string {
+	return string(operator) + string(referenceOpener) + input + string(referenceCloser)
+}
+
+// MappingFuncFor returns a mapping function for use with Expand that
+// implements the expansion semantics defined in the expansion spec; it
+// returns the input string wrapped in the expansion syntax if no mapping
+// for the input is found.
+func MappingFuncFor(context ...map[string]string) func(string) string {
+	return func(input string) string {
+		for _, vars := range context {
+			val, ok := vars[input]
+			if ok {
+				return val
+			}
+		}
+
+		return syntaxWrap(input)
+	}
+}
+
+// Expand replaces variable references in the input string according to
+// the expansion spec using the given mapping function to resolve the
+// values of variables.
+func Expand(input string, mapping func(string) string) string {
+	buf := make([]byte, 0, 2*len(input))
+	checkpoint := 0
+	for cursor := 0; cursor < len(input); cursor++ {
+		if input[cursor] == operator && cursor+1 < len(input) {
+			// Copy the portion of the input string since the last
+			// checkpoint into the buffer
+			buf = append(buf, input[checkpoint:cursor]...)
+
+			// Attempt to read the variable name as defined by the
+			// syntax from the input string
+			read, isVar, advance := tryReadVariableName(input[cursor+1:])
+
+			if isVar {
+				// We were able to read a variable name correctly;
+				// apply the mapping to the variable name and copy the
+				// bytes into the buffer
+				buf = append(buf, mapping(read)...)
+			} else {
+				// Not a variable name; copy the read bytes into the buffer
+				buf = append(buf, read...)
+			}
+
+			// Advance the cursor in the input string to account for
+			// bytes consumed to read the variable name expression
+			cursor += advance
+
+			// Advance the checkpoint in the input string
+			checkpoint = cursor + 1
+		}
+	}
+
+	// Return the buffer and any remaining unwritten bytes in the
+	// input string.
+	return string(buf) + input[checkpoint:]
+}
+
+// tryReadVariableName attempts to read a variable name from the input
+// string and returns the content read from the input, whether that content
+// represents a variable name to perform mapping on, and the number of bytes
+// consumed in the input string.
+//
+// The input string is assumed not to contain the initial operator.
+func tryReadVariableName(input string) (string, bool, int) {
+	switch input[0] {
+	case operator:
+		// Escaped operator; return it.
+		return input[0:1], false, 1
+	case referenceOpener:
+		// Scan to expression closer
+		for i := 1; i < len(input); i++ {
+			if input[i] == referenceCloser {
+				return input[1:i], true, i + 1
+			}
+		}
+
+		// Incomplete reference; return it.
+		return string(operator) + string(referenceOpener), false, 1
+	default:
+		// Not the beginning of an expression, ie, an operator
+		// that doesn't begin an expression.  Return the operator
+		// and the first rune in the string.
+		return (string(operator) + string(input[0])), false, 1
+	}
+}

third_party/golang/expansion/expand_test.go

+package expansion
+
+import (
+	"testing"
+
+	"github.com/GoogleCloudPlatform/kubernetes/pkg/api"
+)
+
+func TestMapReference(t *testing.T) {
+	envs := []api.EnvVar{
+		{
+			Name:  "FOO",
+			Value: "bar",
+		},
+		{
+			Name:  "ZOO",
+			Value: "$(FOO)-1",
+		},
+		{
+			Name:  "BLU",
+			Value: "$(ZOO)-2",
+		},
+	}
+
+	declaredEnv := map[string]string{
+		"FOO": "bar",
+		"ZOO": "$(FOO)-1",
+		"BLU": "$(ZOO)-2",
+	}
+
+	serviceEnv := map[string]string{}
+
+	mapping := MappingFuncFor(declaredEnv, serviceEnv)
+
+	for _, env := range envs {
+		declaredEnv[env.Name] = Expand(env.Value, mapping)
+	}
+
+	expectedEnv := map[string]string{
+		"FOO": "bar",
+		"ZOO": "bar-1",
+		"BLU": "bar-1-2",
+	}
+
+	for k, v := range expectedEnv {
+		if e, a := v, declaredEnv[k]; e != a {
+			t.Errorf("Expected %v, got %v", e, a)
+		} else {
+			delete(declaredEnv, k)
+		}
+	}
+
+	if len(declaredEnv) != 0 {
+		t.Errorf("Unexpected keys in declared env: %v", declaredEnv)
+	}
+}
+
+func TestMapping(t *testing.T) {
+	context := map[string]string{
+		"VAR_A":     "A",
+		"VAR_B":     "B",
+		"VAR_C":     "C",
+		"VAR_REF":   "$(VAR_A)",
+		"VAR_EMPTY": "",
+	}
+	mapping := MappingFuncFor(context)
+
+	doExpansionTest(t, mapping)
+}
+
+func TestMappingDual(t *testing.T) {
+	context := map[string]string{
+		"VAR_A":     "A",
+		"VAR_EMPTY": "",
+	}
+	context2 := map[string]string{
+		"VAR_B":   "B",
+		"VAR_C":   "C",
+		"VAR_REF": "$(VAR_A)",
+	}
+	mapping := MappingFuncFor(context, context2)
+
+	doExpansionTest(t, mapping)
+}
+
+func doExpansionTest(t *testing.T, mapping func(string) string) {
+	cases := []struct {
+		name     string
+		input    string
+		expected string
+	}{
+		{
+			name:     "whole string",
+			input:    "$(VAR_A)",
+			expected: "A",
+		},
+		{
+			name:     "repeat",
+			input:    "$(VAR_A)-$(VAR_A)",
+			expected: "A-A",
+		},
+		{
+			name:     "beginning",
+			input:    "$(VAR_A)-1",
+			expected: "A-1",
+		},
+		{
+			name:     "middle",
+			input:    "___$(VAR_B)___",
+			expected: "___B___",
+		},
+		{
+			name:     "end",
+			input:    "___$(VAR_C)",
+			expected: "___C",
+		},
+		{
+			name:     "compound",
+			input:    "$(VAR_A)_$(VAR_B)_$(VAR_C)",
+			expected: "A_B_C",
+		},
+		{
+			name:     "escape & expand",
+			input:    "$$(VAR_B)_$(VAR_A)",
+			expected: "$(VAR_B)_A",
+		},
+		{
+			name:     "compound escape",
+			input:    "$$(VAR_A)_$$(VAR_B)",
+			expected: "$(VAR_A)_$(VAR_B)",
+		},
+		{
+			name:     "mixed in escapes",
+			input:    "f000-$$VAR_A",
+			expected: "f000-$VAR_A",
+		},
+		{
+			name:     "backslash escape ignored",
+			input:    "foo\\$(VAR_C)bar",
+			expected: "foo\\Cbar",
+		},
+		{
+			name:     "backslash escape ignored",
+			input:    "foo\\\\$(VAR_C)bar",
+			expected: "foo\\\\Cbar",
+		},
+		{
+			name:     "lots of backslashes",
+			input:    "foo\\\\\\\\$(VAR_A)bar",
+			expected: "foo\\\\\\\\Abar",
+		},
+		{
+			name:     "nested var references",
+			input:    "$(VAR_A$(VAR_B))",
+			expected: "$(VAR_A$(VAR_B))",
+		},
+		{
+			name:     "nested var references second type",
+			input:    "$(VAR_A$(VAR_B)",
+			expected: "$(VAR_A$(VAR_B)",
+		},
+		{
+			name:     "value is a reference",
+			input:    "$(VAR_REF)",
+			expected: "$(VAR_A)",
+		},
+		{
+			name:     "value is a reference x 2",
+			input:    "%%$(VAR_REF)--$(VAR_REF)%%",
+			expected: "%%$(VAR_A)--$(VAR_A)%%",
+		},
+		{
+			name:     "empty var",
+			input:    "foo$(VAR_EMPTY)bar",
+			expected: "foobar",
+		},
+		{
+			name:     "unterminated expression",
+			input:    "foo$(VAR_Awhoops!",
+			expected: "foo$(VAR_Awhoops!",
+		},
+		{
+			name:     "expression without operator",
+			input:    "f00__(VAR_A)__",
+			expected: "f00__(VAR_A)__",
+		},
+		{
+			name:     "shell special vars pass through",
+			input:    "$?_boo_$!",
+			expected: "$?_boo_$!",
+		},
+		{
+			name:     "bare operators are ignored",
+			input:    "$VAR_A",
+			expected: "$VAR_A",
+		},
+		{
+			name:     "undefined vars are passed through",
+			input:    "$(VAR_DNE)",
+			expected: "$(VAR_DNE)",
+		},
+		{
+			name:     "multiple (even) operators, var undefined",
+			input:    "$$$$$$(BIG_MONEY)",
+			expected: "$$$(BIG_MONEY)",
+		},
+		{
+			name:     "multiple (even) operators, var defined",
+			input:    "$$$$$$(VAR_A)",
+			expected: "$$$(VAR_A)",
+		},
+		{
+			name:     "multiple (odd) operators, var undefined",
+			input:    "$$$$$$$(GOOD_ODDS)",
+			expected: "$$$$(GOOD_ODDS)",
+		},
+		{
+			name:     "multiple (odd) operators, var defined",
+			input:    "$$$$$$$(VAR_A)",
+			expected: "$$$A",
+		},
+		{
+			name:     "missing open expression",
+			input:    "$VAR_A)",
+			expected: "$VAR_A)",
+		},
+		{
+			name:     "shell syntax ignored",
+			input:    "${VAR_A}",
+			expected: "${VAR_A}",
+		},
+		{
+			name:     "trailing incomplete expression not consumed",
+			input:    "$(VAR_B)_______$(A",
+			expected: "B_______$(A",
+		},
+		{
+			name:     "trailing incomplete expression, no content, is not consumed",
+			input:    "$(VAR_C)_______$(",
+			expected: "C_______$(",
+		},
+		{
+			name:     "operator at end of input string is preserved",
+			input:    "$(VAR_A)foobarzab$",
+			expected: "Afoobarzab$",
+		},
+		{
+			name:     "shell escaped incomplete expr",
+			input:    "foo-\\$(VAR_A",
+			expected: "foo-\\$(VAR_A",
+		},
+		{
+			name:     "lots of $( in middle",
+			input:    "--$($($($($--",
+			expected: "--$($($($($--",
+		},
+		{
+			name:     "lots of $( in beginning",
+			input:    "$($($($($--foo$(",
+			expected: "$($($($($--foo$(",
+		},
+		{
+			name:     "lots of $( at end",
+			input:    "foo0--$($($($(",
+			expected: "foo0--$($($($(",
+		},
+		{
+			name:     "escaped operators in variable names are not escaped",
+			input:    "$(foo$$var)",
+			expected: "$(foo$$var)",
+		},
+		{
+			name:     "newline not expanded",
+			input:    "\n",
+			expected: "\n",
+		},
+	}
+
+	for _, tc := range cases {
+		expanded := Expand(tc.input, mapping)
+		if e, a := tc.expected, expanded; e != a {
+			t.Errorf("%v: expected %q, got %q", tc.name, e, a)
+		}
+	}
+}