fix(gatsby): fix decoding issue in SSR (#35346)

Author: marvinjude

e2e-tests/development-runtime/cypress/integration/ssr.js

@@ -35,6 +35,14 @@ describe(`Static path ('${staticPath}')`, () => {
     cy.getTestElement(`query`).contains(`{}`)
     cy.getTestElement(`params`).contains(`{}`)
   })
+
+  it(`Preserves window.location.search as querystring passed`, () => {
+    const queryString = `?a=b%23&x=y%25&j=`
+    cy.visit(staticPath + queryString).waitForRouteChange()
+    cy.window().then(win => {
+      expect(win.location.search).to.equal(queryString)
+    })
+  })
 })
 
 describe(`Param path ('${paramPath}:param')`, () => {

e2e-tests/production-runtime/cypress/integration/ssr.js

@@ -36,6 +36,14 @@ describe(`Static path ('${staticPath}')`, () => {
     cy.getTestElement(`query`).contains(`{}`)
     cy.getTestElement(`params`).contains(`{}`)
   })
+
+  it("Preserves window.location.search as querystring passed", () => {
+    const queryString = `?a=b%23&x=y%25&j=`
+    cy.visit(staticPath + queryString).waitForRouteChange()
+    cy.window().then(win => {
+      expect(win.location.search).to.equal(queryString)
+    })
+  })
 })
 
 describe(`Param path ('${paramPath}:param')`, () => {

packages/gatsby/src/utils/page-ssr-module/entry.ts

@@ -209,9 +209,14 @@ export async function getData({
     results.pageContext = page.context
 
     let searchString = ``
+
     if (req?.query) {
       const maybeQueryString = Object.entries(req.query)
-        .map(([k, v]) => `${k}=${v}`)
+        .map(
+          ([k, v]) =>
+            // Preserve QueryString encoding
+            `${encodeURIComponent(k)}=${encodeURIComponent(v as string)}`
+        )
         .join(`&`)
       if (maybeQueryString) {
         searchString = `?${maybeQueryString}`