PROJJSON: rename file as projjson.schema.json, and add versionning to it and to exported PROJJSON strings

2 files changed, 25 insertions, 0 deletions

diff --git a/src/iso19111/c_api.cpp b/src/iso19111/c_api.cpp
index d4813091..d27b8800 100644
--- a/src/iso19111/c_api.cpp
+++ b/src/iso19111/c_api.cpp
@@ -1335,6 +1335,8 @@ const char *proj_as_proj_string(PJ_CONTEXT *ctx, const PJ *obj,
  * <li>MULTILINE=YES/NO. Defaults to YES</li>
  * <li>INDENTATION_WIDTH=number. Defauls to 2 (when multiline output is
  * on).</li>
+ * <li>SCHEMA=string. URL to PROJJSON schema. Can be set to empty string to
+ * disable it.</li>
  * </ul>
  * @return a string, or NULL in case of error.
  *
@@ -1359,6 +1361,8 @@ const char *proj_as_projjson(PJ_CONTEXT *ctx, const PJ *obj,
                 formatter->setMultiLine(ci_equal(value, "YES"));
             } else if ((value = getOptionValue(*iter, "INDENTATION_WIDTH="))) {
                 formatter->setIndentationWidth(std::atoi(value));
+            } else if ((value = getOptionValue(*iter, "SCHEMA="))) {
+                formatter->setSchema(value);
             } else {
                 std::string msg("Unknown option :");
                 msg += *iter;
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index 9f4f6061..5ccd9642 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -86,6 +86,10 @@ using json = nlohmann::json;
 
 //! @cond Doxygen_Suppress
 static const std::string emptyString{};
+
+// If changing that value, change it in data/projjson.schema.json as well
+#define PROJJSON_CURRENT_VERSION                                               \
+    "https://proj.org/schemas/v0.1/projjson.schema.json"
 //! @endcond
 
 #if 0
@@ -9103,6 +9107,7 @@ struct JSONFormatter::Private {
     bool allowIDInImmediateChild_ = false;
     bool omitTypeInImmediateChild_ = false;
     bool abridgedTransformation_ = false;
+    std::string schema_ = PROJJSON_CURRENT_VERSION;
 
     std::string result_{};
 
@@ -9148,6 +9153,17 @@ JSONFormatter &JSONFormatter::setIndentationWidth(int width) noexcept {
 
 // ---------------------------------------------------------------------------
 
+/** \brief Set the value of the "$schema" key in the top level object.
+ *
+ * If set to empty string, it will not be written.
+ */
+JSONFormatter &JSONFormatter::setSchema(const std::string &schema) noexcept {
+    d->schema_ = schema;
+    return *this;
+}
+
+// ---------------------------------------------------------------------------
+
 //! @cond Doxygen_Suppress
 
 JSONFormatter::JSONFormatter() : d(internal::make_unique<Private>()) {}
@@ -9188,6 +9204,11 @@ JSONFormatter::ObjectContext::ObjectContext(JSONFormatter &formatter,
                                             const char *objectType, bool hasId)
     : m_formatter(formatter) {
     m_formatter.d->writer_.StartObj();
+    if (m_formatter.d->outputIdStack_.size() == 1 &&
+        !m_formatter.d->schema_.empty()) {
+        m_formatter.d->writer_.AddObjKey("$schema");
+        m_formatter.d->writer_.Add(m_formatter.d->schema_);
+    }
     if (objectType && !m_formatter.d->omitTypeInImmediateChild_) {
         m_formatter.d->writer_.AddObjKey("type");
         m_formatter.d->writer_.Add(objectType);