Use advrefs in gituploadpackinfo (#92)

* add advrefs encoder and parser

* modify advrefs encoder to resemble json encoder

* turn advrefs parser into a decoder

* clean code

* improve documentation

* improve documentation

* clean code

* upgrade to new pktline.Add and add Flush const to easy integration

* gometalinter

* Use packp/advrefs for GitUploadPackInfo parsing

- GitUploadPackInfo now uses packp/advrefs instead of parsing the
  message by itself.

- Capabilities has been moved from clients/common to packp to avoid a
  circular import.

- Cleaning of advrefs_test code.

- Add support for prefix encoding and decoding in advrefs.

* clean advrefs test code

* clean advrefs test code

* clean advrefs test code

* gometalinter

* add pktline encoder

* change pktline.EncodeFlush to pktline.Flush

* make scanner tests use the encoder instead of Pktlines

* check errors on flush and clean constants

* ubstitute the PktLines type with a pktline.Encoder

* use pktline.Encoder in all go-git

* add example of pktline.Encodef()

* add package overview

* documentation

* support symbolic links other than HEAD

* simplify decoding of shallows

* packp: fix mcuadros comments

- all abbreviates removed (by visual inspection, some may remain)
- all empty maps are initialized using make
- simplify readRef with a switch
- make decodeShallow malformed error more verbose
- add pktline.Encoder.encodeLine
- remove infamous panic in checkPayloadLength by refactoring out
  the whole function

1 files changed, 136 insertions, 0 deletions

diff --git a/formats/packp/capabilities.go b/formats/packp/capabilities.go
new file mode 100644
index 0000000..d77c2fa
--- /dev/null
+++ b/formats/packp/capabilities.go
@@ -0,0 +1,136 @@
+package packp
+
+import (
+	"fmt"
+	"sort"
+	"strings"
+)
+
+// Capabilities contains all the server capabilities
+// https://github.com/git/git/blob/master/Documentation/technical/protocol-capabilities.txt
+type Capabilities struct {
+	m map[string]*Capability
+	o []string
+}
+
+// Capability represents a server capability
+type Capability struct {
+	Name   string
+	Values []string
+}
+
+// NewCapabilities returns a new Capabilities struct
+func NewCapabilities() *Capabilities {
+	return &Capabilities{
+		m: make(map[string]*Capability),
+	}
+}
+
+func (c *Capabilities) IsEmpty() bool {
+	return len(c.o) == 0
+}
+
+// Decode decodes a string
+func (c *Capabilities) Decode(raw string) {
+	params := strings.Split(raw, " ")
+	for _, p := range params {
+		s := strings.SplitN(p, "=", 2)
+
+		var value string
+		if len(s) == 2 {
+			value = s[1]
+		}
+
+		c.Add(s[0], value)
+	}
+}
+
+// Get returns the values for a capability
+func (c *Capabilities) Get(capability string) *Capability {
+	return c.m[capability]
+}
+
+// Set sets a capability removing the values
+func (c *Capabilities) Set(capability string, values ...string) {
+	if _, ok := c.m[capability]; ok {
+		delete(c.m, capability)
+	}
+
+	c.Add(capability, values...)
+}
+
+// Add adds a capability, values are optional
+func (c *Capabilities) Add(capability string, values ...string) {
+	if !c.Supports(capability) {
+		c.m[capability] = &Capability{Name: capability}
+		c.o = append(c.o, capability)
+	}
+
+	if len(values) == 0 {
+		return
+	}
+
+	c.m[capability].Values = append(c.m[capability].Values, values...)
+}
+
+// Supports returns true if capability is present
+func (c *Capabilities) Supports(capability string) bool {
+	_, ok := c.m[capability]
+	return ok
+}
+
+// SymbolicReference returns the reference for a given symbolic reference
+func (c *Capabilities) SymbolicReference(sym string) string {
+	if !c.Supports("symref") {
+		return ""
+	}
+
+	for _, symref := range c.Get("symref").Values {
+		parts := strings.Split(symref, ":")
+		if len(parts) != 2 {
+			continue
+		}
+
+		if parts[0] == sym {
+			return parts[1]
+		}
+	}
+
+	return ""
+}
+
+// Sorts capabilities in increasing order of their name
+func (c *Capabilities) Sort() {
+	sort.Strings(c.o)
+}
+
+func (c *Capabilities) String() string {
+	if len(c.o) == 0 {
+		return ""
+	}
+
+	var o string
+	for _, key := range c.o {
+		cap := c.m[key]
+
+		added := false
+		for _, value := range cap.Values {
+			if value == "" {
+				continue
+			}
+
+			added = true
+			o += fmt.Sprintf("%s=%s ", key, value)
+		}
+
+		if len(cap.Values) == 0 || !added {
+			o += key + " "
+		}
+	}
+
+	if len(o) == 0 {
+		return o
+	}
+
+	return o[:len(o)-1]
+}