pstuifzand/ekster

// Package linkheader provides functions for parsing HTTP Link headers
package linkheader

import (
    "fmt"
    "strings"
)

// A Link is a single URL and related parameters
type Link struct {
    URL    string
    Rel    string
    Params map[string]string
}

// HasParam returns if a Link has a particular parameter or not
func (l Link) HasParam(key string) bool {
    for p := range l.Params {
        if p == key {
            return true
        }
    }
    return false
}

// Param returns the value of a parameter if it exists
func (l Link) Param(key string) string {
    for k, v := range l.Params {
        if key == k {
            return v
        }
    }
    return ""
}

// String returns the string representation of a link
func (l Link) String() string {

    p := make([]string, 0, len(l.Params))
    for k, v := range l.Params {
        p = append(p, fmt.Sprintf("%s=\"%s\"", k, v))
    }
    if l.Rel != "" {
        p = append(p, fmt.Sprintf("%s=\"%s\"", "rel", l.Rel))
    }
    return fmt.Sprintf("<%s>; %s", l.URL, strings.Join(p, "; "))
}

// Links is a slice of Link structs
type Links []Link

// FilterByRel filters a group of Links by the provided Rel attribute
func (l Links) FilterByRel(r string) Links {
    links := make(Links, 0)
    for _, link := range l {
        if link.Rel == r {
            links = append(links, link)
        }
    }
    return links
}

// String returns the string representation of multiple Links
// for use in HTTP responses etc
func (l Links) String() string {
    if l == nil {
        return fmt.Sprint(nil)
    }

    var strs []string
    for _, link := range l {
        strs = append(strs, link.String())
    }
    return strings.Join(strs, ", ")
}

// Parse parses a raw Link header in the form:
//   <url>; rel="foo", <url>; rel="bar"; wat="dis"
// returning a slice of Link structs
func Parse(raw string) Links {
    var links Links

    // One chunk: <url>; rel="foo"
    for _, chunk := range strings.Split(raw, ",") {

        link := Link{URL: "", Rel: "", Params: make(map[string]string)}

        // Figure out what each piece of the chunk is
        for _, piece := range strings.Split(chunk, ";") {

            piece = strings.Trim(piece, " ")
            if piece == "" {
                continue
            }

            // URL
            if piece[0] == '<' && piece[len(piece)-1] == '>' {
                link.URL = strings.Trim(piece, "<>")
                continue
            }

            // Params
            key, val := parseParam(piece)
            if key == "" {
                continue
            }

            // Special case for rel
            if strings.ToLower(key) == "rel" {
                link.Rel = val
            } else {
                link.Params[key] = val
            }
        }

        if link.URL != "" {
            links = append(links, link)
        }
    }

    return links
}

// ParseMultiple is like Parse, but accepts a slice of headers
// rather than just one header string
func ParseMultiple(headers []string) Links {
    links := make(Links, 0)
    for _, header := range headers {
        links = append(links, Parse(header)...)
    }
    return links
}

// parseParam takes a raw param in the form key="val" and
// returns the key and value as seperate strings
func parseParam(raw string) (key, val string) {

    parts := strings.SplitN(raw, "=", 2)
    if len(parts) != 2 {
        return "", ""
    }

    key = parts[0]
    val = strings.Trim(parts[1], "\"")

    return key, val

}