protocol/packp: capabilities new Capability entity and List struct, test improvements (#144)

* protocol/pakp: capabilities new Capability entity and List struct, test improvements

* etc: example cloud-config file

* removing sorting from List.String

3 files changed, 551 insertions, 0 deletions

diff --git a/plumbing/protocol/packp/capability/capability.go b/plumbing/protocol/packp/capability/capability.go
new file mode 100644
index 0000000..06fbfca
--- /dev/null
+++ b/plumbing/protocol/packp/capability/capability.go
@@ -0,0 +1,249 @@
+package capability
+
+// Capability describes a server or client capability
+type Capability string
+
+func (n Capability) String() string {
+	return string(n)
+}
+
+const (
+	// MultiACK capability allows the server to return "ACK obj-id continue" as
+	// soon as it finds a commit that it can use as a common base, between the
+	// client's wants and the client's have set.
+	//
+	// By sending this early, the server can potentially head off the client
+	// from walking any further down that particular branch of the client's
+	// repository history.  The client may still need to walk down other
+	// branches, sending have lines for those, until the server has a
+	// complete cut across the DAG, or the client has said "done".
+	//
+	// Without multi_ack, a client sends have lines in --date-order until
+	// the server has found a common base.  That means the client will send
+	// have lines that are already known by the server to be common, because
+	// they overlap in time with another branch that the server hasn't found
+	// a common base on yet.
+	//
+	// For example suppose the client has commits in caps that the server
+	// doesn't and the server has commits in lower case that the client
+	// doesn't, as in the following diagram:
+	//
+	//        +---- u ---------------------- x
+	//       /              +----- y
+	//      /              /
+	//     a -- b -- c -- d -- E -- F
+	//        \
+	// 	+--- Q -- R -- S
+	//
+	// If the client wants x,y and starts out by saying have F,S, the server
+	// doesn't know what F,S is.  Eventually the client says "have d" and
+	// the server sends "ACK d continue" to let the client know to stop
+	// walking down that line (so don't send c-b-a), but it's not done yet,
+	// it needs a base for x. The client keeps going with S-R-Q, until a
+	// gets reached, at which point the server has a clear base and it all
+	// ends.
+	//
+	// Without multi_ack the client would have sent that c-b-a chain anyway,
+	// interleaved with S-R-Q.
+	MultiACK Capability = "multi_ack"
+	// MultiACKDetailed is an extension of multi_ack that permits client to
+	// better understand the server's in-memory state.
+	MultiACKDetailed Capability = "multi_ack_detailed"
+	// NoDone should only be used with the smart HTTP protocol. If
+	// multi_ack_detailed and no-done are both present, then the sender is
+	// free to immediately send a pack following its first "ACK obj-id ready"
+	// message.
+	//
+	// Without no-done in the smart HTTP protocol, the server session would
+	// end and the client has to make another trip to send "done" before
+	// the server can send the pack. no-done removes the last round and
+	// thus slightly reduces latency.
+	NoDone Capability = "no-done"
+	// ThinPack is one with deltas which reference base objects not
+	// contained within the pack (but are known to exist at the receiving
+	// end). This can reduce the network traffic significantly, but it
+	// requires the receiving end to know how to "thicken" these packs by
+	// adding the missing bases to the pack.
+	//
+	// The upload-pack server advertises 'thin-pack' when it can generate
+	// and send a thin pack. A client requests the 'thin-pack' capability
+	// when it understands how to "thicken" it, notifying the server that
+	// it can receive such a pack. A client MUST NOT request the
+	// 'thin-pack' capability if it cannot turn a thin pack into a
+	// self-contained pack.
+	//
+	// Receive-pack, on the other hand, is assumed by default to be able to
+	// handle thin packs, but can ask the client not to use the feature by
+	// advertising the 'no-thin' capability. A client MUST NOT send a thin
+	// pack if the server advertises the 'no-thin' capability.
+	//
+	// The reasons for this asymmetry are historical. The receive-pack
+	// program did not exist until after the invention of thin packs, so
+	// historically the reference implementation of receive-pack always
+	// understood thin packs. Adding 'no-thin' later allowed receive-pack
+	// to disable the feature in a backwards-compatible manner.
+	ThinPack Capability = "thin-pack"
+	// Sideband means that server can send, and client understand multiplexed
+	// progress reports and error info interleaved with the packfile itself.
+	//
+	// These two options are mutually exclusive. A modern client always
+	// favors Sideband64k.
+	//
+	// Either mode indicates that the packfile data will be streamed broken
+	// up into packets of up to either 1000 bytes in the case of 'side_band',
+	// or 65520 bytes in the case of 'side_band_64k'. Each packet is made up
+	// of a leading 4-byte pkt-line length of how much data is in the packet,
+	// followed by a 1-byte stream code, followed by the actual data.
+	//
+	// The stream code can be one of:
+	//
+	//  1 - pack data
+	//  2 - progress messages
+	//  3 - fatal error message just before stream aborts
+	//
+	// The "side-band-64k" capability came about as a way for newer clients
+	// that can handle much larger packets to request packets that are
+	// actually crammed nearly full, while maintaining backward compatibility
+	// for the older clients.
+	//
+	// Further, with side-band and its up to 1000-byte messages, it's actually
+	// 999 bytes of payload and 1 byte for the stream code. With side-band-64k,
+	// same deal, you have up to 65519 bytes of data and 1 byte for the stream
+	// code.
+	//
+	// The client MUST send only maximum of one of "side-band" and "side-
+	// band-64k".  Server MUST diagnose it as an error if client requests
+	// both.
+	Sideband    Capability = "side-band"
+	Sideband64k Capability = "side-band-64k"
+	// OFSDelta server can send, and client understand PACKv2 with delta
+	// referring to its base by position in pack rather than by an obj-id. That
+	// is, they can send/read OBJ_OFS_DELTA (aka type 6) in a packfile.
+	OFSDelta Capability = "ofs-delta"
+	// Agent the server may optionally send this capability to notify the client
+	// that the server is running version `X`. The client may optionally return
+	// its own agent string by responding with an `agent=Y` capability (but it
+	// MUST NOT do so if the server did not mention the agent capability). The
+	// `X` and `Y` strings may contain any printable ASCII characters except
+	// space (i.e., the byte range 32 < x < 127), and are typically of the form
+	// "package/version" (e.g., "git/1.8.3.1"). The agent strings are purely
+	// informative for statistics and debugging purposes, and MUST NOT be used
+	// to programmatically assume the presence or absence of particular features.
+	Agent Capability = "agent"
+	// Shallow capability adds "deepen", "shallow" and "unshallow" commands to
+	// the  fetch-pack/upload-pack protocol so clients can request shallow
+	// clones.
+	Shallow Capability = "shallow"
+	// DeepenSince adds "deepen-since" command to fetch-pack/upload-pack
+	// protocol so the client can request shallow clones that are cut at a
+	// specific time, instead of depth. Internally it's equivalent of doing
+	// "rev-list --max-age=<timestamp>" on the server side. "deepen-since"
+	// cannot be used with "deepen".
+	DeepenSince Capability = "deepen-since"
+	// DeepenNot adds "deepen-not" command to fetch-pack/upload-pack
+	// protocol so the client can request shallow clones that are cut at a
+	// specific revision, instead of depth. Internally it's equivalent of
+	// doing "rev-list --not <rev>" on the server side. "deepen-not"
+	// cannot be used with "deepen", but can be used with "deepen-since".
+	DeepenNot Capability = "deepen-not"
+	// DeepenRelative if this capability is requested by the client, the
+	// semantics of "deepen" command is changed. The "depth" argument is the
+	// depth from the current shallow boundary, instead of the depth from
+	// remote refs.
+	DeepenRelative Capability = "deepen-relative"
+	// NoProgress the client was started with "git clone -q" or something, and
+	// doesn't want that side band 2. Basically the client just says "I do not
+	// wish to receive stream 2 on sideband, so do not send it to me, and if
+	// you did, I will drop it on the floor anyway".  However, the sideband
+	// channel 3 is still used for error responses.
+	NoProgress Capability = "no-progress"
+	// IncludeTag capability is about sending annotated tags if we are
+	// sending objects they point to.  If we pack an object to the client, and
+	// a tag object points exactly at that object, we pack the tag object too.
+	// In general this allows a client to get all new annotated tags when it
+	// fetches a branch, in a single network connection.
+	//
+	// Clients MAY always send include-tag, hardcoding it into a request when
+	// the server advertises this capability. The decision for a client to
+	// request include-tag only has to do with the client's desires for tag
+	// data, whether or not a server had advertised objects in the
+	// refs/tags/* namespace.
+	//
+	// Servers MUST pack the tags if their referrant is packed and the client
+	// has requested include-tags.
+	//
+	// Clients MUST be prepared for the case where a server has ignored
+	// include-tag and has not actually sent tags in the pack.  In such
+	// cases the client SHOULD issue a subsequent fetch to acquire the tags
+	// that include-tag would have otherwise given the client.
+	//
+	// The server SHOULD send include-tag, if it supports it, regardless
+	// of whether or not there are tags available.
+	IncludeTag Capability = "include-tag"
+	// ReportStatus the receive-pack process can receive a 'report-status'
+	// capability, which tells it that the client wants a report of what
+	// happened after a packfile upload and reference update. If the pushing
+	// client requests this capability, after unpacking and updating references
+	// the server will respond with whether the packfile unpacked successfully
+	// and if each reference was updated successfully. If any of those were not
+	// successful, it will send back an error message.  See pack-protocol.txt
+	// for example messages.
+	ReportStatus Capability = "report-status"
+	// DeleteRefs If the server sends back this capability, it means that
+	// it is capable of accepting a zero-id value as the target
+	// value of a reference update.  It is not sent back by the client, it
+	// simply informs the client that it can be sent zero-id values
+	// to delete references
+	DeleteRefs Capability = "delete-refs"
+	// Quiet If the receive-pack server advertises this capability, it is
+	// capable of silencing human-readable progress output which otherwise may
+	// be shown when processing the received pack. A send-pack client should
+	// respond with the 'quiet' capability to suppress server-side progress
+	// reporting if the local progress reporting is also being suppressed
+	// (e.g., via `push -q`, or if stderr does not go to a tty).
+	Quiet Capability = "quiet"
+	// Atomic If the server sends this capability it is capable of accepting
+	// atomic pushes. If the pushing client requests this capability, the server
+	// will update the refs in one atomic transaction. Either all refs are
+	// updated or none.
+	Atomic Capability = "atomic"
+	// PushOptions If the server sends this capability it is able to accept
+	// push options after the update commands have been sent, but before the
+	// packfile is streamed. If the pushing client requests this capability,
+	// the server will pass the options to the pre- and post- receive hooks
+	// that process this push request.
+	PushOptions Capability = "push-options"
+	// AllowTipSHA1InWant if the upload-pack server advertises this capability,
+	// fetch-pack may send "want" lines with SHA-1s that exist at the server but
+	// are not advertised by upload-pack.
+	AllowTipSHA1InWant Capability = "allow-tip-sha1-in-want"
+	// AllowReachableSHA1InWant if the upload-pack server advertises this
+	// capability, fetch-pack may send "want" lines with SHA-1s that exist at
+	// the server but are not advertised by upload-pack.
+	AllowReachableSHA1InWant Capability = "allow-reachable-sha1-in-want"
+	// PushCert the receive-pack server that advertises this capability is
+	// willing to accept a signed push certificate, and asks the <nonce> to be
+	// included in the push certificate.  A send-pack client MUST NOT
+	// send a push-cert packet unless the receive-pack server advertises
+	// this capability.
+	PushCert Capability = "push-cert"
+	// SymRef symbolic reference support for better negotiation.
+	SymRef Capability = "symref"
+)
+
+var valid = map[Capability]bool{
+	MultiACK: true, MultiACKDetailed: true, NoDone: true, ThinPack: true,
+	Sideband: true, Sideband64k: true, OFSDelta: true, Agent: true,
+	Shallow: true, DeepenSince: true, DeepenNot: true, DeepenRelative: true,
+	NoProgress: true, IncludeTag: true, ReportStatus: true, DeleteRefs: true,
+	Quiet: true, Atomic: true, PushOptions: true, AllowTipSHA1InWant: true,
+	AllowReachableSHA1InWant: true, PushCert: true, SymRef: true,
+}
+
+var requiresArgument = map[Capability]bool{
+	Agent: true, PushCert: true, SymRef: true,
+}
+
+var multipleArgument = map[Capability]bool{
+	SymRef: true,
+}
diff --git a/plumbing/protocol/packp/capability/list.go b/plumbing/protocol/packp/capability/list.go
new file mode 100644
index 0000000..73d1f25
--- /dev/null
+++ b/plumbing/protocol/packp/capability/list.go
@@ -0,0 +1,161 @@
+package capability
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"strings"
+)
+
+var (
+	// ErrUnknownCapability is returned if a unknown capability is given
+	ErrUnknownCapability = errors.New("unknown capability")
+	// ErrArgumentsRequired is returned if no arguments are giving with a
+	// capability that requires arguments
+	ErrArgumentsRequired = errors.New("arguments required")
+	// ErrArguments is returned if arguments are given with a capabilities that
+	// not supports arguments
+	ErrArguments = errors.New("arguments not allowed")
+	// ErrEmtpyArgument is returned when an empty value is given
+	ErrEmtpyArgument = errors.New("empty argument")
+	// ErrMultipleArguments multiple argument given to a capabilities that not
+	// support it
+	ErrMultipleArguments = errors.New("multiple arguments not allowed")
+)
+
+// List represents a list of capabilities
+type List struct {
+	m    map[Capability]*entry
+	sort []string
+}
+
+type entry struct {
+	Name   Capability
+	Values []string
+}
+
+// NewList returns a new List of capabilities
+func NewList() *List {
+	return &List{
+		m: make(map[Capability]*entry),
+	}
+}
+
+// IsEmpty returns true if the List is empty
+func (l *List) IsEmpty() bool {
+	return len(l.sort) == 0
+}
+
+// Decode decodes list of capabilities from raw into the list
+func (l *List) Decode(raw []byte) error {
+	for _, data := range bytes.Split(raw, []byte{' '}) {
+		pair := bytes.SplitN(data, []byte{'='}, 2)
+
+		c := Capability(pair[0])
+		if len(pair) == 1 {
+			if err := l.Add(c); err != nil {
+				return err
+			}
+
+			continue
+		}
+
+		if err := l.Add(c, string(pair[1])); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Get returns the values for a capability
+func (l *List) Get(capability Capability) []string {
+	if _, ok := l.m[capability]; !ok {
+		return nil
+	}
+
+	return l.m[capability].Values
+}
+
+// Set sets a capability removing the previous values
+func (l *List) Set(capability Capability, values ...string) error {
+	if _, ok := l.m[capability]; ok {
+		delete(l.m, capability)
+	}
+
+	return l.Add(capability, values...)
+}
+
+// Add adds a capability, values are optional
+func (l *List) Add(c Capability, values ...string) error {
+	if err := l.validate(c, values); err != nil {
+		return err
+	}
+
+	if !l.Supports(c) {
+		l.m[c] = &entry{Name: c}
+		l.sort = append(l.sort, c.String())
+	}
+
+	if len(values) == 0 {
+		return nil
+	}
+
+	if !multipleArgument[c] && len(l.m[c].Values) > 0 {
+		return ErrMultipleArguments
+	}
+
+	l.m[c].Values = append(l.m[c].Values, values...)
+	return nil
+}
+
+func (l *List) validate(c Capability, values []string) error {
+	if _, ok := valid[c]; !ok {
+		return ErrUnknownCapability
+	}
+
+	if requiresArgument[c] && len(values) == 0 {
+		return ErrArgumentsRequired
+	}
+
+	if !requiresArgument[c] && len(values) != 0 {
+		return ErrArguments
+	}
+
+	if !multipleArgument[c] && len(values) > 1 {
+		return ErrMultipleArguments
+	}
+
+	for _, v := range values {
+		if v == "" {
+			return ErrEmtpyArgument
+		}
+	}
+
+	return nil
+}
+
+// Supports returns true if capability is present
+func (l *List) Supports(capability Capability) bool {
+	_, ok := l.m[capability]
+	return ok
+}
+
+// String generates the capabilities strings, the capabilities are sorted in
+// insertion order
+func (l *List) String() string {
+	var o []string
+	for _, key := range l.sort {
+		cap := l.m[Capability(key)]
+		if len(cap.Values) == 0 {
+			o = append(o, key)
+			continue
+		}
+
+		for _, value := range cap.Values {
+			o = append(o, fmt.Sprintf("%s=%s", key, value))
+		}
+	}
+
+	return strings.Join(o, " ")
+}
diff --git a/plumbing/protocol/packp/capability/list_test.go b/plumbing/protocol/packp/capability/list_test.go
new file mode 100644
index 0000000..6d350b0
--- /dev/null
+++ b/plumbing/protocol/packp/capability/list_test.go
@@ -0,0 +1,141 @@
+package capability
+
+import (
+	"testing"
+
+	check "gopkg.in/check.v1"
+)
+
+func Test(t *testing.T) { check.TestingT(t) }
+
+type SuiteCapabilities struct{}
+
+var _ = check.Suite(&SuiteCapabilities{})
+
+func (s *SuiteCapabilities) TestIsEmpty(c *check.C) {
+	cap := NewList()
+	c.Assert(cap.IsEmpty(), check.Equals, true)
+}
+
+func (s *SuiteCapabilities) TestDecode(c *check.C) {
+	cap := NewList()
+	err := cap.Decode([]byte("symref=foo symref=qux thin-pack"))
+	c.Assert(err, check.IsNil)
+
+	c.Assert(cap.m, check.HasLen, 2)
+	c.Assert(cap.Get(SymRef), check.DeepEquals, []string{"foo", "qux"})
+	c.Assert(cap.Get(ThinPack), check.IsNil)
+}
+
+func (s *SuiteCapabilities) TestDecodeWithErrArguments(c *check.C) {
+	cap := NewList()
+	err := cap.Decode([]byte("thin-pack=foo"))
+	c.Assert(err, check.Equals, ErrArguments)
+}
+
+func (s *SuiteCapabilities) TestDecodeWithEqual(c *check.C) {
+	cap := NewList()
+	err := cap.Decode([]byte("agent=foo=bar"))
+	c.Assert(err, check.IsNil)
+
+	c.Assert(cap.m, check.HasLen, 1)
+	c.Assert(cap.Get(Agent), check.DeepEquals, []string{"foo=bar"})
+}
+
+func (s *SuiteCapabilities) TestDecodeWithErrUnknownCapability(c *check.C) {
+	cap := NewList()
+	err := cap.Decode([]byte("foo"))
+	c.Assert(err, check.Equals, ErrUnknownCapability)
+}
+
+func (s *SuiteCapabilities) TestString(c *check.C) {
+	cap := NewList()
+	cap.Set(Agent, "bar")
+	cap.Set(SymRef, "foo:qux")
+	cap.Set(ThinPack)
+
+	c.Assert(cap.String(), check.Equals, "agent=bar symref=foo:qux thin-pack")
+}
+
+func (s *SuiteCapabilities) TestStringSort(c *check.C) {
+	cap := NewList()
+	cap.Set(Agent, "bar")
+	cap.Set(SymRef, "foo:qux")
+	cap.Set(ThinPack)
+
+	c.Assert(cap.String(), check.Equals, "agent=bar symref=foo:qux thin-pack")
+}
+
+func (s *SuiteCapabilities) TestSet(c *check.C) {
+	cap := NewList()
+	err := cap.Add(SymRef, "foo", "qux")
+	c.Assert(err, check.IsNil)
+	err = cap.Set(SymRef, "bar")
+	c.Assert(err, check.IsNil)
+
+	c.Assert(cap.m, check.HasLen, 1)
+	c.Assert(cap.Get(SymRef), check.DeepEquals, []string{"bar"})
+}
+
+func (s *SuiteCapabilities) TestSetEmpty(c *check.C) {
+	cap := NewList()
+	err := cap.Set(Agent, "bar")
+	c.Assert(err, check.IsNil)
+
+	c.Assert(cap.Get(Agent), check.HasLen, 1)
+}
+
+func (s *SuiteCapabilities) TestGetEmpty(c *check.C) {
+	cap := NewList()
+	c.Assert(cap.Get(Agent), check.HasLen, 0)
+}
+
+func (s *SuiteCapabilities) TestAdd(c *check.C) {
+	cap := NewList()
+	err := cap.Add(SymRef, "foo", "qux")
+	c.Assert(err, check.IsNil)
+
+	err = cap.Add(ThinPack)
+	c.Assert(err, check.IsNil)
+
+	c.Assert(cap.String(), check.Equals, "symref=foo symref=qux thin-pack")
+}
+
+func (s *SuiteCapabilities) TestAddErrUnknownCapability(c *check.C) {
+	cap := NewList()
+	err := cap.Add(Capability("foo"))
+	c.Assert(err, check.Equals, ErrUnknownCapability)
+}
+
+func (s *SuiteCapabilities) TestAddErrArgumentsRequired(c *check.C) {
+	cap := NewList()
+	err := cap.Add(SymRef)
+	c.Assert(err, check.Equals, ErrArgumentsRequired)
+}
+
+func (s *SuiteCapabilities) TestAddErrArgumentsNotAllowed(c *check.C) {
+	cap := NewList()
+	err := cap.Add(OFSDelta, "foo")
+	c.Assert(err, check.Equals, ErrArguments)
+}
+
+func (s *SuiteCapabilities) TestAddErrArgumendts(c *check.C) {
+	cap := NewList()
+	err := cap.Add(SymRef, "")
+	c.Assert(err, check.Equals, ErrEmtpyArgument)
+}
+
+func (s *SuiteCapabilities) TestAddErrMultipleArguments(c *check.C) {
+	cap := NewList()
+	err := cap.Add(Agent, "foo")
+	c.Assert(err, check.IsNil)
+
+	err = cap.Add(Agent, "bar")
+	c.Assert(err, check.Equals, ErrMultipleArguments)
+}
+
+func (s *SuiteCapabilities) TestAddErrMultipleArgumentsAtTheSameTime(c *check.C) {
+	cap := NewList()
+	err := cap.Add(Agent, "foo", "bar")
+	c.Assert(err, check.Equals, ErrMultipleArguments)
+}