1 files changed, 153 insertions, 0 deletions
diff --git a/completer/completer.go b/completer/completer.go
new file mode 100644
index 0000000..baa897d
--- /dev/null
+++ b/completer/completer.go
@@ -0,0 +1,153 @@
+package completer
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"log"
+	"net/mail"
+	"os/exec"
+	"strings"
+
+	"github.com/google/shlex"
+)
+
+// A Completer is used to autocomplete text inputs based on the configured
+// completion commands.
+type Completer struct {
+	// AddressBookCmd is the command to run for completing email addresses. This
+	// command must output one completion on each line with fields separated by a
+	// tab character. The first field must be the address, and the second field,
+	// if present, the contact name. Only the email address field is required.
+	// The name field is optional. Additional fields are ignored.
+	AddressBookCmd string
+
+	errHandler func(error)
+	logger     *log.Logger
+}
+
+// A CompleteFunc accepts a string to be completed and returns a slice of
+// possible completions.
+type CompleteFunc func(string) []string
+
+// New creates a new Completer with the specified address book command.
+func New(addressBookCmd string, errHandler func(error), logger *log.Logger) *Completer {
+	return &Completer{
+		AddressBookCmd: addressBookCmd,
+		errHandler:     errHandler,
+		logger:         logger,
+	}
+}
+
+// ForHeader returns a CompleteFunc appropriate for the specified mail header. In
+// the case of To, From, etc., the completer will get completions from the
+// configured address book command. For other headers, a noop completer will be
+// returned. If errors arise during completion, the errHandler will be called.
+func (c *Completer) ForHeader(h string) CompleteFunc {
+	if isAddressHeader(h) {
+		if c.AddressBookCmd == "" {
+			return nil
+		}
+		// wrap completeAddress in an error handler
+		return func(s string) []string {
+			completions, err := c.completeAddress(s)
+			if err != nil {
+				c.handleErr(err)
+				return []string{}
+			}
+			return completions
+		}
+	}
+	return nil
+}
+
+// isAddressHeader determines whether the address completer should be used for
+// header h.
+func isAddressHeader(h string) bool {
+	switch strings.ToLower(h) {
+	case "to", "from", "cc", "bcc":
+		return true
+	}
+	return false
+}
+
+// completeAddress uses the configured address book completion command to fetch
+// completions for the specified string, returning a slice of completions or an
+// error.
+func (c *Completer) completeAddress(s string) ([]string, error) {
+	cmd, err := c.getAddressCmd(s)
+	if err != nil {
+		return nil, err
+	}
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, fmt.Errorf("stdout: %v", err)
+	}
+	if err := cmd.Start(); err != nil {
+		return nil, fmt.Errorf("cmd start: %v", err)
+	}
+	completions, err := readCompletions(stdout)
+	if err != nil {
+		return nil, fmt.Errorf("read completions: %v", err)
+	}
+
+	// Wait returns an error if the exit status != 0, which some completion
+	// programs will do to signal no matches. We don't want to spam the user with
+	// spurious error messages, so we'll ignore any errors that arise at this
+	// point.
+	if err := cmd.Wait(); err != nil {
+		c.logger.Printf("completion error: %v", err)
+	}
+
+	return completions, nil
+}
+
+// getAddressCmd constructs an exec.Cmd based on the configured command and
+// specified query.
+func (c *Completer) getAddressCmd(s string) (*exec.Cmd, error) {
+	if strings.TrimSpace(c.AddressBookCmd) == "" {
+		return nil, fmt.Errorf("no command configured")
+	}
+	queryCmd := strings.Replace(c.AddressBookCmd, "%s", s, -1)
+	parts, err := shlex.Split(queryCmd)
+	if err != nil {
+		return nil, fmt.Errorf("could not lex command")
+	}
+	if len(parts) < 1 {
+		return nil, fmt.Errorf("empty command")
+	}
+	if len(parts) > 1 {
+		return exec.Command(parts[0], parts[1:]...), nil
+	}
+	return exec.Command(parts[0]), nil
+}
+
+// readCompletions reads a slice of completions from r line by line. Each line
+// must consist of tab-delimited fields. Only the first field (the email
+// address field) is required, the second field (the contact name) is optional,
+// and subsequent fields are ignored.
+func readCompletions(r io.Reader) ([]string, error) {
+	buf := bufio.NewReader(r)
+	completions := []string{}
+	for {
+		line, err := buf.ReadString('\n')
+		if err == io.EOF {
+			return completions, nil
+		} else if err != nil {
+			return nil, err
+		}
+		parts := strings.SplitN(line, "\t", 3)
+		if addr, err := mail.ParseAddress(parts[0]); err == nil {
+			if len(parts) > 1 {
+				addr.Name = parts[1]
+			}
+			completions = append(completions, addr.String())
+		}
+	}
+}
+
+func (c *Completer) handleErr(err error) {
+	if c.errHandler != nil {
+		c.errHandler(err)
+	}
+}