From 06b56941257864c365198a1c73ff6581947e43dc Mon Sep 17 00:00:00 2001
From: Tom Wright <contact@tomwright.me>
Date: Wed, 15 Apr 2020 17:44:17 +0100
Subject: [PATCH] Add GET handler for diagram generation

---
 README.md        |  7 ++++-
 internal/http.go | 75 +++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 67 insertions(+), 15 deletions(-)

diff --git a/README.md b/README.md
index 839ac8f..33862c8 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ Start the HTTP server:
 go run cmd/app/main.go --mermaid=./mermaidcli/node_modules/.bin/mmdc --in=./in --out=./out
 ```
 
-Send CURL request to generate a diagram:
+Send CURL request to generate a diagram via `POST`:
 ```
 curl --location --request POST 'http://localhost:80/generate' \
 --header 'Content-Type: text/plain' \
@@ -24,5 +24,10 @@ curl --location --request POST 'http://localhost:80/generate' \
 '
 ```
 
+Or send CURL request to generate a diagram via `GET`... send in url encoded data under the `data` query param:
+```
+curl --location --request GET 'http://localhost:80/generate?data=graph%20LR%0A%0A%20%20%20%20A--%3EB%0A%20%20%20%20B--%3EC%0A%20%20%20%20C--%3ED%0A%20%20%20%20C--%3EF%0A'
+```
+
 Inline-style: 
 ![Example request in Postman](example.png "Example request in Postman")
\ No newline at end of file
diff --git a/internal/http.go b/internal/http.go
index 0176c7d..4cb1611 100644
--- a/internal/http.go
+++ b/internal/http.go
@@ -5,6 +5,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"net/url"
+	"strings"
 )
 
 func writeJSON(rw http.ResponseWriter, value interface{}, status int) {
@@ -33,31 +35,76 @@ func writeErr(rw http.ResponseWriter, err error, status int) {
 	}, status)
 }
 
+// URLParam is the URL parameter getDiagramFromGET uses to look for data.
+const URLParam = "data"
+
+func getDiagramFromGET(rw http.ResponseWriter, r *http.Request) *Diagram {
+	if r.Method != http.MethodGet {
+		writeErr(rw, fmt.Errorf("expected HTTP method GET"), http.StatusBadRequest)
+		return nil
+	}
+
+	queryVal := strings.TrimSpace(r.URL.Query().Get(URLParam))
+	if queryVal == "" {
+		writeErr(rw, fmt.Errorf("missing data"), http.StatusBadRequest)
+		return nil
+	}
+	data, err := url.QueryUnescape(queryVal)
+	if err != nil {
+		writeErr(rw, fmt.Errorf("could not read query param: %s", err), http.StatusBadRequest)
+		return nil
+	}
+
+	// Create a diagram from the description
+	d := NewDiagram([]byte(data))
+	return d
+}
+
+func getDiagramFromPOST(rw http.ResponseWriter, r *http.Request) *Diagram {
+	if r.Method != http.MethodPost {
+		writeErr(rw, fmt.Errorf("expected HTTP method POST"), http.StatusBadRequest)
+		return nil
+	}
+	// Get description from request body
+	bytes, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		writeErr(rw, fmt.Errorf("could not read body: %s", err), http.StatusInternalServerError)
+		return nil
+	}
+
+	// Create a diagram from the description
+	d := NewDiagram(bytes)
+	return d
+}
+
+// GenerateHTTPHandler returns a HTTP handler used to generate a diagram.
 func GenerateHTTPHandler(generator Generator) func(rw http.ResponseWriter, r *http.Request) {
 	return func(rw http.ResponseWriter, r *http.Request) {
-		if r.Method != http.MethodPost {
-			writeErr(rw, fmt.Errorf("expected HTTP method POST"), http.StatusBadRequest)
-			return
-		}
-		// Get description from request body
-		bytes, err := ioutil.ReadAll(r.Body)
-		if err != nil {
-			writeErr(rw, fmt.Errorf("could not read body: %s", err), http.StatusInternalServerError)
-			return
-		}
+		var diagram *Diagram
 
-		// Create a diagram from the description
-		d := NewDiagram(bytes)
+		switch r.Method {
+		case http.MethodGet:
+			diagram = getDiagramFromGET(rw, r)
+		case http.MethodPost:
+			diagram = getDiagramFromPOST(rw, r)
+		default:
+			writeErr(rw, fmt.Errorf("unexpected HTTP method %s", r.Method), http.StatusBadRequest)
+			return
+		}
+		if diagram == nil {
+			writeErr(rw, fmt.Errorf("could not create diagram"), http.StatusInternalServerError)
+			return
+		}
 
 		// Generate the diagram
-		if err := generator.Generate(d); err != nil {
+		if err := generator.Generate(diagram); err != nil {
 			writeErr(rw, fmt.Errorf("could not generate diagram: %s", err), http.StatusInternalServerError)
 			return
 		}
 
 		// Output the diagram as an SVG.
 		// We assume generate always generates an SVG at this point in time.
-		diagramBytes, err := ioutil.ReadFile(d.Output)
+		diagramBytes, err := ioutil.ReadFile(diagram.Output)
 		if err != nil {
 			writeErr(rw, fmt.Errorf("could not read diagram bytes: %s", err), http.StatusInternalServerError)
 			return