From 8eabf0f4036efd861679d3a064870c1466e11c01 Mon Sep 17 00:00:00 2001
From: Christian Muehlhaeuser <muesli@gmail.com>
Date: Tue, 26 Nov 2019 00:08:06 +0100
Subject: [PATCH] Handle relative URLs in markdown, when a BaseURL is provided

---
 github.go |  4 ++--
 gitlab.go |  4 ++--
 main.go   | 37 +++++++++++++++++++++++++------------
 3 files changed, 29 insertions(+), 16 deletions(-)

diff --git a/github.go b/github.go
index 2a7661a..1b04da7 100644
--- a/github.go
+++ b/github.go
@@ -22,7 +22,7 @@ func isGitHubURL(s string) (string, bool) {
 }
 
 // findGitHubREADME tries to find the correct README filename in a repository
-func findGitHubREADME(s string) (*http.Response, error) {
+func findGitHubREADME(s string) (*Source, error) {
 	u, err := url.ParseRequestURI(s)
 	if err != nil {
 		return nil, err
@@ -39,7 +39,7 @@ func findGitHubREADME(s string) (*http.Response, error) {
 		}
 
 		if resp.StatusCode == http.StatusOK {
-			return resp, nil
+			return &Source{resp.Body, v.String()}, nil
 		}
 	}
 
diff --git a/gitlab.go b/gitlab.go
index 2c5676e..7c6dfa5 100644
--- a/gitlab.go
+++ b/gitlab.go
@@ -22,7 +22,7 @@ func isGitLabURL(s string) (string, bool) {
 }
 
 // findGitLabREADME tries to find the correct README filename in a repository
-func findGitLabREADME(s string) (*http.Response, error) {
+func findGitLabREADME(s string) (*Source, error) {
 	u, err := url.ParseRequestURI(s)
 	if err != nil {
 		return nil, err
@@ -38,7 +38,7 @@ func findGitLabREADME(s string) (*http.Response, error) {
 		}
 
 		if resp.StatusCode == http.StatusOK {
-			return resp, nil
+			return &Source{resp.Body, v.String()}, nil
 		}
 	}
 
diff --git a/main.go b/main.go
index b5244a8..dffb5cc 100644
--- a/main.go
+++ b/main.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"path/filepath"
 
 	"github.com/mattn/go-isatty"
 	"github.com/muesli/go-wordwrap"
@@ -31,24 +32,29 @@ var (
 	width uint
 )
 
-func readerFromArg(s string) (io.ReadCloser, error) {
+type Source struct {
+	reader io.ReadCloser
+	URL    string
+}
+
+func readerFromArg(s string) (*Source, error) {
 	if s == "-" {
-		return os.Stdin, nil
+		return &Source{reader: os.Stdin}, nil
 	}
 
 	if u, ok := isGitHubURL(s); ok {
-		resp, err := findGitHubREADME(u)
+		src, err := findGitHubREADME(u)
 		if err != nil {
 			return nil, err
 		}
-		return resp.Body, nil
+		return src, nil
 	}
 	if u, ok := isGitLabURL(s); ok {
-		resp, err := findGitLabREADME(u)
+		src, err := findGitLabREADME(u)
 		if err != nil {
 			return nil, err
 		}
-		return resp.Body, nil
+		return src, nil
 	}
 
 	if u, err := url.ParseRequestURI(s); err == nil {
@@ -63,21 +69,22 @@ func readerFromArg(s string) (io.ReadCloser, error) {
 		if resp.StatusCode != http.StatusOK {
 			return nil, fmt.Errorf("HTTP status %d", resp.StatusCode)
 		}
-		return resp.Body, nil
+		return &Source{resp.Body, u.String()}, nil
 	}
 
 	if len(s) == 0 {
 		for _, v := range readmeNames {
 			r, err := os.Open(v)
 			if err == nil {
-				return r, nil
+				return &Source{reader: r}, nil
 			}
 		}
 
 		return nil, errors.New("missing markdown source")
 	}
 
-	return os.Open(s)
+	r, err := os.Open(s)
+	return &Source{reader: r}, err
 }
 
 func execute(cmd *cobra.Command, args []string) error {
@@ -85,12 +92,12 @@ func execute(cmd *cobra.Command, args []string) error {
 	if len(args) > 0 {
 		arg = args[0]
 	}
-	in, err := readerFromArg(arg)
+	src, err := readerFromArg(arg)
 	if err != nil {
 		return err
 	}
-	defer in.Close()
-	b, _ := ioutil.ReadAll(in)
+	defer src.reader.Close()
+	b, _ := ioutil.ReadAll(src.reader)
 
 	r := gold.NewPlainTermRenderer()
 	if isatty.IsTerminal(os.Stdout.Fd()) {
@@ -100,6 +107,12 @@ func execute(cmd *cobra.Command, args []string) error {
 		}
 	}
 
+	u, err := url.ParseRequestURI(src.URL)
+	if err == nil {
+		u.Path = filepath.Dir(u.Path)
+		r.BaseURL = u.String() + "/"
+	}
+
 	out := r.RenderBytes(b)
 	fmt.Printf("%s", wordwrap.WrapString(string(out), width))
 	return nil