/*
 *
 * Copyright 2014 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

// Package metadata define the structure of the metadata supported by gRPC library.
// Please refer to https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md
// for more information about custom-metadata.
package metadata // import "google.golang.org/grpc/metadata"

import (
	"context"
	"fmt"
	"sort"
	"strings"

	"google.golang.org/grpc/internal"
)

func init() {
	internal.FromOutgoingContextRaw = fromOutgoingContextRaw
}

// DecodeKeyValue returns k, v, nil.
//
// Deprecated: use k and v directly instead.
func DecodeKeyValue(k, v string) (string, string, error) {
	return k, v, nil
}

// MD is a mapping from metadata keys to values. Users should use the following
// two convenience functions New and Pairs to generate MD.
type MD map[string][]string

// New creates an MD from a given key-value map.
//
// Only the following ASCII characters are allowed in keys:
//   - digits: 0-9
//   - uppercase letters: A-Z (normalized to lower)
//   - lowercase letters: a-z
//   - special characters: -_.
//
// Uppercase letters are automatically converted to lowercase.
//
// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
// result in errors if set in metadata.
func New(m map[string]string) MD {
	md := make(MD, len(m))
	for k, val := range m {
		key := strings.ToLower(k)
		md[key] = append(md[key], val)
	}
	return md
}

// Pairs returns an MD formed by the mapping of key, value ...
// Pairs panics if len(kv) is odd.
//
// Only the following ASCII characters are allowed in keys:
//   - digits: 0-9
//   - uppercase letters: A-Z (normalized to lower)
//   - lowercase letters: a-z
//   - special characters: -_.
//
// Uppercase letters are automatically converted to lowercase.
//
// Keys beginning with "grpc-" are reserved for grpc-internal use only and may
// result in errors if set in metadata.
func Pairs(kv ...string) MD {
	if len(kv)%2 == 1 {
		panic(fmt.Sprintf("metadata: Pairs got the odd number of input pairs for metadata: %d", len(kv)))
	}
	md := make(MD, len(kv)/2)
	for i := 0; i < len(kv); i += 2 {
		key := strings.ToLower(kv[i])
		md[key] = append(md[key], kv[i+1])
	}
	return md
}

// loggableMetadataKeys is the set of metadata keys whose values are known not
// to carry credentials or other sensitive data, and are therefore safe to print
// verbatim in String. Values for any key not in this set are redacted. Keys are
// in metadata's canonical lowercase form.
//
// The list is intentionally restricted to standardized gRPC and HTTP/2 protocol
// headers. Everything else, including all application-defined keys, is
// censored.
// Note that this list might change as we add/remove support for
// metadata types.
var loggableMetadataKeys = map[string]bool{
	"content-type":               true,
	"te":                         true,
	"user-agent":                 true,
	"grpc-encoding":              true,
	"grpc-accept-encoding":       true,
	"grpc-timeout":               true,
	"grpc-status":                true,
	"grpc-message-type":          true,
	"grpc-previous-rpc-attempts": true,
	"grpc-retry-pushback-ms":     true,
}

// String implements fmt.Stringer to allow metadata to be printed when stored in
// a context.
//
// To avoid accidentally leaking credentials or other sensitive data (for
// example via log(md), or by logging a value that happens to contain metadata),
// String reports only keys on an allowlist of standardized, non-sensitive
// protocol headers (see loggableMetadataKeys). Every other key is omitted
// entirely, along with its values, because a key name may itself be sensitive;
// only the number of omitted keys is reported, as "<N redacted>". This is a
// best-effort guard against accidents, not a security boundary: a caller that
// genuinely wants the full contents can still print map[string][]string(md)
// directly.
//
// Note that this only affects verbs that use the Stringer, such as %v and %s.
// The %#v verb prints the underlying map with all values and is not redacted.
// Users should not rely on the output of this method to be stable
// # Experimental
//
// Notice: This API is EXPERIMENTAL and may be changed or removed in a later
// release.
func (md MD) String() string {
	keys := make([]string, 0, len(md))
	for k := range md {
		if loggableMetadataKeys[strings.ToLower(k)] {
			keys = append(keys, k)
		}
	}
	sort.Strings(keys)

	var sb strings.Builder
	sb.WriteString("map[")
	for i, k := range keys {
		if i > 0 {
			sb.WriteByte(' ')
		}
		fmt.Fprintf(&sb, "%s:%v", k, md[k])
	}
	if redacted := len(md) - len(keys); redacted > 0 {
		if len(keys) > 0 {
			sb.WriteByte(' ')
		}
		fmt.Fprintf(&sb, "<%d redacted>", redacted)
	}
	sb.WriteByte(']')
	return sb.String()
}

// Len returns the number of items in md.
func (md MD) Len() int {
	return len(md)
}

// Copy returns a copy of md.
func (md MD) Copy() MD {
	out := make(MD, len(md))
	for k, v := range md {
		out[k] = copyOf(v)
	}
	return out
}

// Get obtains the values for a given key.
//
// k is converted to lowercase before searching in md.
func (md MD) Get(k string) []string {
	k = strings.ToLower(k)
	return md[k]
}

// Set sets the value of a given key with a slice of values.
//
// k is converted to lowercase before storing in md.
func (md MD) Set(k string, vals ...string) {
	if len(vals) == 0 {
		return
	}
	k = strings.ToLower(k)
	md[k] = vals
}

// Append adds the values to key k, not overwriting what was already stored at
// that key.
//
// k is converted to lowercase before storing in md.
func (md MD) Append(k string, vals ...string) {
	if len(vals) == 0 {
		return
	}
	k = strings.ToLower(k)
	md[k] = append(md[k], vals...)
}

// Delete removes the values for a given key k which is converted to lowercase
// before removing it from md.
func (md MD) Delete(k string) {
	k = strings.ToLower(k)
	delete(md, k)
}

// Join joins any number of mds into a single MD.
//
// The order of values for each key is determined by the order in which the mds
// containing those values are presented to Join.
func Join(mds ...MD) MD {
	out := MD{}
	for _, md := range mds {
		for k, v := range md {
			out[k] = append(out[k], v...)
		}
	}
	return out
}

type mdIncomingKey struct{}
type mdOutgoingKey struct{}

// NewIncomingContext creates a new context with incoming md attached. md must
// not be modified after calling this function.
func NewIncomingContext(ctx context.Context, md MD) context.Context {
	return context.WithValue(ctx, mdIncomingKey{}, md)
}

// NewOutgoingContext creates a new context with outgoing md attached. If used
// in conjunction with AppendToOutgoingContext, NewOutgoingContext will
// overwrite any previously-appended metadata. md must not be modified after
// calling this function.
func NewOutgoingContext(ctx context.Context, md MD) context.Context {
	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md})
}

// AppendToOutgoingContext returns a new context with the provided kv merged
// with any existing metadata in the context. Please refer to the documentation
// of Pairs for a description of kv.
func AppendToOutgoingContext(ctx context.Context, kv ...string) context.Context {
	if len(kv)%2 == 1 {
		panic(fmt.Sprintf("metadata: AppendToOutgoingContext got an odd number of input pairs for metadata: %d", len(kv)))
	}
	md, _ := ctx.Value(mdOutgoingKey{}).(rawMD)
	added := make([][]string, len(md.added)+1)
	copy(added, md.added)
	kvCopy := make([]string, 0, len(kv))
	for i := 0; i < len(kv); i += 2 {
		kvCopy = append(kvCopy, strings.ToLower(kv[i]), kv[i+1])
	}
	added[len(added)-1] = kvCopy
	return context.WithValue(ctx, mdOutgoingKey{}, rawMD{md: md.md, added: added})
}

// FromIncomingContext returns the incoming metadata in ctx if it exists.
//
// All keys in the returned MD are lowercase.
func FromIncomingContext(ctx context.Context) (MD, bool) {
	md, ok := ctx.Value(mdIncomingKey{}).(MD)
	if !ok {
		return nil, false
	}
	out := make(MD, len(md))
	for k, v := range md {
		// We need to manually convert all keys to lower case, because MD is a
		// map, and there's no guarantee that the MD attached to the context is
		// created using our helper functions.
		key := strings.ToLower(k)
		out[key] = copyOf(v)
	}
	return out, true
}

// ValueFromIncomingContext returns the metadata value corresponding to the metadata
// key from the incoming metadata if it exists. Keys are matched in a case insensitive
// manner.
func ValueFromIncomingContext(ctx context.Context, key string) []string {
	md, ok := ctx.Value(mdIncomingKey{}).(MD)
	if !ok {
		return nil
	}

	if v, ok := md[key]; ok {
		return copyOf(v)
	}
	for k, v := range md {
		// Case insensitive comparison: MD is a map, and there's no guarantee
		// that the MD attached to the context is created using our helper
		// functions.
		if strings.EqualFold(k, key) {
			return copyOf(v)
		}
	}
	return nil
}

func copyOf(v []string) []string {
	vals := make([]string, len(v))
	copy(vals, v)
	return vals
}

// fromOutgoingContextRaw returns the un-merged, intermediary contents of rawMD.
//
// Remember to perform strings.ToLower on the keys, for both the returned MD (MD
// is a map, there's no guarantee it's created using our helper functions) and
// the extra kv pairs (AppendToOutgoingContext doesn't turn them into
// lowercase).
func fromOutgoingContextRaw(ctx context.Context) (MD, [][]string, bool) {
	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
	if !ok {
		return nil, nil, false
	}

	return raw.md, raw.added, true
}

// FromOutgoingContext returns the outgoing metadata in ctx if it exists.
//
// All keys in the returned MD are lowercase.
func FromOutgoingContext(ctx context.Context) (MD, bool) {
	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
	if !ok {
		return nil, false
	}

	mdSize := len(raw.md)
	for i := range raw.added {
		mdSize += len(raw.added[i]) / 2
	}

	out := make(MD, mdSize)
	for k, v := range raw.md {
		// We need to manually convert all keys to lower case, because MD is a
		// map, and there's no guarantee that the MD attached to the context is
		// created using our helper functions.
		key := strings.ToLower(k)
		out[key] = copyOf(v)
	}
	for _, added := range raw.added {
		if len(added)%2 == 1 {
			panic(fmt.Sprintf("metadata: FromOutgoingContext got an odd number of input pairs for metadata: %d", len(added)))
		}

		for i := 0; i < len(added); i += 2 {
			key := strings.ToLower(added[i])
			out[key] = append(out[key], added[i+1])
		}
	}
	return out, ok
}

// ValueFromOutgoingContext returns the metadata value corresponding to the
// metadata key from the outgoing metadata if it exists. Keys are matched in a
// case-insensitive manner.
//
// Unlike FromOutgoingContext, this does not copy the entire outgoing metadata.
func ValueFromOutgoingContext(ctx context.Context, key string) []string {
	raw, ok := ctx.Value(mdOutgoingKey{}).(rawMD)
	if !ok {
		return nil
	}

	key = strings.ToLower(key)
	// Unlike ValueFromIncomingContext, this can't return as soon as raw.md is
	// checked: raw.added still needs to be walked and accumulated regardless.
	// The else below prevents that from overwriting an exact match with an
	// unrelated case-insensitive one.
	var matchedMD []string
	if v, ok := raw.md[key]; ok {
		matchedMD = v
	} else {
		for k, v := range raw.md {
			// Case insensitive comparison: MD is a map, and there's no
			// guarantee that the MD attached to the context is created using
			// our helper functions.
			if strings.EqualFold(k, key) {
				matchedMD = v
				break
			}
		}
	}

	// Defer allocating vals until raw.added actually has a match, so a match
	// found only in raw.md doesn't pay for both a copyOf and a growing
	// append.
	var vals []string
	for _, added := range raw.added {
		if len(added)%2 == 1 {
			panic(fmt.Sprintf("metadata: ValueFromOutgoingContext got an odd number of input pairs for metadata: %d", len(added)))
		}

		// Case insensitive, like FromOutgoingContext: added isn't guaranteed
		// lowercase, though AppendToOutgoingContext already lowercases it in
		// practice, so try the cheap exact match first.
		for i := 0; i < len(added); i += 2 {
			if added[i] == key || strings.EqualFold(added[i], key) {
				if vals == nil {
					vals = make([]string, 0, len(matchedMD)+1)
					vals = append(vals, matchedMD...)
				}
				vals = append(vals, added[i+1])
			}
		}
	}

	if vals == nil && matchedMD != nil {
		return copyOf(matchedMD)
	}
	return vals
}

type rawMD struct {
	md    MD
	added [][]string
}