config: add default path, customized configs.

A customised config is an ini file with a [default] section and some
other name sections; a config file is loaded from the default section
with any keys in the named section being added in, overriding keys in
the host. This allows for, e.g. setting different paths based on the
host name or operating system.

config/iniconf/iniconf.go

@@ -0,0 +1,223 @@
+package iniconf
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+)
+
+// ConfigMap is shorthand for the type used as a config struct.
+type ConfigMap map[string]map[string]string
+
+var (
+	configSection    = regexp.MustCompile(`^\s*\[\s*(\w+)\s*\]\s*$`)
+	quotedConfigLine = regexp.MustCompile(`^\s*(\w+)\s*=\s*["'](.*)["']\s*$`)
+	configLine       = regexp.MustCompile(`^\s*(\w+)\s*=\s*(.*)\s*$`)
+	commentLine      = regexp.MustCompile(`^#.*$`)
+	blankLine        = regexp.MustCompile(`^\s*$`)
+)
+
+// DefaultSection is the label for the default ini file section.
+var DefaultSection = "default"
+
+// ParseFile attempts to load the named config file.
+func ParseFile(fileName string) (cfg ConfigMap, err error) {
+	var file *os.File
+	file, err = os.Open(fileName)
+	if err != nil {
+		return
+	}
+	defer file.Close()
+	return ParseReader(file)
+}
+
+// ParseReader reads a configuration from an io.Reader.
+func ParseReader(r io.Reader) (cfg ConfigMap, err error) {
+	cfg = ConfigMap{}
+	buf := bufio.NewReader(r)
+
+	var (
+		line           string
+		longLine       bool
+		currentSection string
+		lineBytes      []byte
+		isPrefix       bool
+	)
+
+	for {
+		err = nil
+		lineBytes, isPrefix, err = buf.ReadLine()
+		if io.EOF == err {
+			err = nil
+			break
+		} else if err != nil {
+			break
+		} else if isPrefix {
+			line += string(lineBytes)
+
+			longLine = true
+			continue
+		} else if longLine {
+			line += string(lineBytes)
+			longLine = false
+		} else {
+			line = string(lineBytes)
+		}
+
+		if commentLine.MatchString(line) {
+			continue
+		} else if blankLine.MatchString(line) {
+			continue
+		} else if configSection.MatchString(line) {
+			section := configSection.ReplaceAllString(line,
+				"$1")
+			if section == "" {
+				err = fmt.Errorf("invalid structure in file")
+				break
+			} else if !cfg.SectionInConfig(section) {
+				cfg[section] = make(map[string]string, 0)
+			}
+			currentSection = section
+		} else if configLine.MatchString(line) {
+			regex := configLine
+			if quotedConfigLine.MatchString(line) {
+				regex = quotedConfigLine
+			}
+			if currentSection == "" {
+				currentSection = DefaultSection
+				if !cfg.SectionInConfig(currentSection) {
+					cfg[currentSection] = map[string]string{}
+				}
+			}
+			key := regex.ReplaceAllString(line, "$1")
+			val := regex.ReplaceAllString(line, "$2")
+			if key == "" {
+				continue
+			}
+			cfg[currentSection][key] = val
+		} else {
+			err = fmt.Errorf("invalid config file")
+			break
+		}
+	}
+	return
+}
+
+// SectionInConfig determines whether a section is in the configuration.
+func (c ConfigMap) SectionInConfig(section string) bool {
+	_, ok := c[section]
+	return ok
+}
+
+// ListSections returns the list of sections in the config map.
+func (c ConfigMap) ListSections() (sections []string) {
+	for section := range c {
+		sections = append(sections, section)
+	}
+	return
+}
+
+// WriteFile writes out the configuration to a file.
+func (c ConfigMap) WriteFile(filename string) (err error) {
+	file, err := os.Create(filename)
+	if err != nil {
+		return
+	}
+	defer file.Close()
+
+	for _, section := range c.ListSections() {
+		sName := fmt.Sprintf("[ %s ]\n", section)
+		_, err = file.Write([]byte(sName))
+		if err != nil {
+			return
+		}
+
+		for k, v := range c[section] {
+			line := fmt.Sprintf("%s = %s\n", k, v)
+			_, err = file.Write([]byte(line))
+			if err != nil {
+				return
+			}
+		}
+		_, err = file.Write([]byte{0x0a})
+		if err != nil {
+			return
+		}
+	}
+	return
+}
+
+// AddSection creates a new section in the config map.
+func (c ConfigMap) AddSection(section string) {
+	if nil != c[section] {
+		c[section] = map[string]string{}
+	}
+}
+
+// AddKeyVal adds a key value pair to a config map.
+func (c ConfigMap) AddKeyVal(section, key, val string) {
+	if section == "" {
+		section = DefaultSection
+	}
+
+	if nil == c[section] {
+		c.AddSection(section)
+	}
+
+	c[section][key] = val
+}
+
+// GetValue retrieves the value from a key map.
+func (c ConfigMap) GetValue(section, key string) (val string, present bool) {
+	if c == nil {
+		return
+	}
+
+	if section == "" {
+		section = DefaultSection
+	}
+
+	_, ok := c[section]
+	if !ok {
+		return
+	}
+
+	val, present = c[section][key]
+	return
+}
+
+// GetValueDefault retrieves the value from a key map if present,
+// otherwise the default value.
+func (c ConfigMap) GetValueDefault(section, key, value string) (val string) {
+	kval, ok := c.GetValue(section, key)
+	if !ok {
+		return value
+	}
+	return kval
+}
+
+// SectionKeys returns the sections in the config map.
+func (c ConfigMap) SectionKeys(section string) (keys []string, present bool) {
+	if c == nil {
+		return nil, false
+	}
+
+	if section == "" {
+		section = DefaultSection
+	}
+
+	cm := c
+	s, ok := cm[section]
+	if !ok {
+		return nil, false
+	}
+
+	keys = make([]string, 0, len(s))
+	for key := range s {
+		keys = append(keys, key)
+	}
+
+	return keys, true
+}